Asklemmy

Unlockable bootloader, removable battery, headphone jack, being assembled with SCREWS rather than GLUE.

Removable battery is the big one. I had a phone where they only cost like $15, so I could take 2 of them on a trip and last a week w/o charging.

Headphone jack, dedicated fingerprint reader, removable battery, physical sim card trays

Edit: expandable storage

Physical keyboards.

IR blaster. You could have a universal remote app and control any tv from my palm PDA

Fingerprint sensor on the back of the phone. So you'd pick it up and your finger would naturally fall on the sensor, so that by the time you look at the screen, it's unlocked.

Headphone jack

3.5mm headphone jack.

I miss the notification lights. One of my first true smart phones was the original oneplus. It was fun setting up custom colors for different types of notifications and came in handy every now and then

3.5 jack

Replaceable batteries.

Headphone jacks and the ability to expand available memory using SD cards.

IR Blasters!

I feel like I'm the only one who used them or cares that they were quietly phased out of phones.

You used to be able to use your phone as a universal remote. Being able to control my TV, sound system, ceiling fan, and lights all from my phone was so convenient! Plus if you were stuck in like a waiting room and they had ads or garbage like Fox News on, you could change the channel or turn it off completely. It was an incredibly useful feature to me, but I guess barely anyone else used since it was removed from phones without any complaints.

Except me. I'm complaining!

Being able reach the entire screen with one hand... Even with larger hands, reaching across a 6 inch screen with my thumb is bullshit and uncomfortable as fuck. I miss my iPhone 4S

Notification LED.

Small sizes

Multicolour notification LEDS - customisable for each app

Smaller camera bumps and less cameras in general - not everyone wants or needs to be a professional photographer.

Plastic bodies, with removable batteries via covers.

I don't know how many current phones support it but mine doesn't... Extendable storage via micro sd

Customisable vibration patterns for different contacts and apps - I remember how super old early Android Xperia phones being able to do this (alongside the LED mentioned above). I used to think this was stock android, I guess not. But if it was, why did they remove it, same guess for LED

Tactile buttons

Once I get my next phone, I'll miss the headphones jack.

Battery life, even with massive batteries, modern phones only last a day while older phones could last up to a week between charges.

Privacy

Headphone jack and IR blaster

FM radio. Sometimes it was nice to listen to the radio on my phone.

IR transmitter, removable batteries (but they will come back), the notification LED.

Headphone jack for sure. Like 90% of my phone usage is either listening to music or watching videos, so decent audio is like the only thing I care about lol.

This may sound dumb... An old Samsung phone I had years ago, came with alarms that gradually faded in. The most memorable, started with the ocean, and the seagulls... Then there was a fog horn in the distance. Slowly the horn got closer, and closer... Until it was all you could hear, and your alarm was going off.

I've looked everywhere for the sound file... It must be Locked away in a basement at Samsung somewhere.

One day I'll find it

Removable batteries

Batteries that lasted a week.

Multi-colored LED notification light - better yet the Nexus One trackball + multi-colored LED light in one.

Headphone jack is always nice. I don't use it anymore, if anything USB-C dongle is fine.

An indestructible phone. Nokia and Sony Ericsson had some phones that were stronger than a brick. This weak glass sucks.

Removable batteries :(

I had an htc one that could transmit IR signals meaning you could mess with TVs and other simple wireless electronics. You could also use the headphone wire as an actual radio antenna.

I like where phones are now for the most part, but the thing I miss the most is that magic moment of what leaps and bounds new technology/form factor/whatever was being incorporated into a new phone. Like when the iPhone was first announced or when Motorola announced (and marketed the hell out of) the original Droid - I can still hear the boot up sound.

I remember the debates and arguments had when the first 4+” phone was released and how it was “way too big” compared to the ideal sized 3.5” iPhone. The idea of swiping to type!? What a breakthrough! A fingerprint scanner to unlock your phone, that took like three or four tries some times and was met with skepticism by others.

Now I feel like, despite how monstrously capable are phones are now compared to even five years ago, there’s just not as much of a spark anymore. New phones are iterative and have been for a while. Bendable displays are sort of neat, but just doesn’t quite tap the same bit of magic for me.

I miss the gboard of 5 years ago when typo correction was spooky good.

I miss uploading my own songs to Google music.

I miss easily flashable bootloadera and roms.

I miss the three virtual navigation buttons.

I miss setting different notification dot colors for different apps.

I miss setting different notification sounds for different people.

Modern computers are slow.

Specifically, modern computers have inherently more delay time between the keyboard (or other input devices), the software, and the display than much-older (1980s) computers. This means that it is not possible to create games that are as responsive to player inputs as the arcade, console, or microcomputer games of the past.

USB is slow. HDMI is slow.

I miss the IR blaster in the headphone Jack of my old s5 every day

I miss the times when different phones had character. Even phones of the same company looked completely different:

Now it’s just the same rectangle stretched different ways and maybe different color sides.

User-replaceable batteries.

Physical keyboard. I miss touch typing one handed.

I loved how older versions of Android (and afaik iOS as well) could set the album cover of the currently played song as the lockscreen background.

It's a tiny and maybe completely unnecessary feature, but i loved it.

Rear mounted fingerprint sensor 3.5mm Audio port

I refuse to use a phone without a headphone jack.

Honestly, I miss my hardware keyboard and not giving up so much screen real estate while typing.

Physical buttons. Sometimes an app or the OS itself will fuck up and not show you the home or back button for example.

I would miss headphone jacks but any phone worth buying still comes with those... for now

I miss the notification LED on older Galaxy phones.

The back fingerprint reader used to have gestures, so swiping down on it could for example open the notification shade. Was really good for not having greasy fingerprints on your screen

I really miss small phones. Used to be a time when manufacturers were competing to make them as small as possible and Dell's 5" phone was universally mocked as too big.

Removable battery and LED notification lights.

Welp - I'm thoroughly convinced to never upgrade from my BlackBerry Key1. I will hang on to my multi-day battery life, 3.5mm headphone jack, keyboard, notification LED, fingerprint reader, and cheap, replaceable parts till phones stop being a fucking thing.

I recognize this list of "Gone for everyone but me" may not be perfectly in the spirit of this question, but all the same: Thanks everyone! :D

Not really a feature. But I really I wish I could upgrade my phone. Like, get a new camera with better quality or a new battery with higher energy density in an older phone. Stuff like this.

The IR blaster on my galaxy s6. Not the most used feature, but when the Air BnB didn’t have all the remotes it was a life saver.