Technically, a phone is also a computer, albeit a not so powerful one and that's why you can still code with it. I actually started doing web development with my phone a couple of years ago and it was easy for me but just like you said, after using an IDE, it's now very difficult to use my phone to code, mostly because of the flexibility that comes with using an IDE. Termux is a very good terminal for android, it works even better if your phone is rooted