I have used Emacs on mobile for years. Works great in Termux on Android for instance. I use it daily and with the same .emacs.d (synced using git) as I use on computers, with just a few conditionals in init.el to not load too many bloated dependencies for things I am unlikely to use on my phone anyway.

I can second this, Termux + Emacs turned my phone back into a personal computer.

It is helpful to add extra keys to your touch keyboard, which you can do by editing your termux properties file (see https://wiki.termux.com/wiki/Touch_Keyboard). Helpful when you don't have a hardware keyboard available.