I have emacs installed in Termux on Android. Termux provides an extra button bar above the main keyboard for things like Ctrl, arrow keys, Esc, Meta which makes emacs just about usable in Termux. Without those things it would be unusable!
Without the magic button bar you'd need the hackers keyboard which works very well on tablets but it is just a bit squashed for phones unless you use them in landscape.
https://play.google.com/store/apps/details?id=org.pocketwork...