For me its the ‘Knock Code’ that LG had on their phones (I really wish LG still made at least the V series phones)
Basically there was a four-square area and you set up a sequence of where you would tap to unlock the phone. That set of squares was only shown when you set up the code
Then, to unlock your phone, you would tap those areas in the sequence you set up (even with the screen off).
Fingerprint readers are nice, but I really do miss the knock code
Edit: did find this article with a way to do the knock code, but if done wrong, could brick your phone I guess.
Plus, article is from 2014. When I looked at XDA’s info on it (they also being the developers) it looks like development on it is over, but individual modules may or may not still be supported by their devs
I don’t actually miss much, but I also don’t really use my phone a whole lot. I have a smartphone, but it’s pretty close to factory settings. I don’t really install apps outside Line, I very rarely make calls on it. It probably gets used for transit directions/maps, mail, and Line 90% of the time.
Maybe not a specific feature, but I do dislike the general trend towards large and larger phones/screens. I must prefer the smaller phones we used to have; I know Apple had their smaller phone lines recently but I think they didn’t do particularly well.