Not iPhone but Android+Termux and only short code examples.

Customization is key.

Edit

PS: I'm using Emacs since my second semester at university.

There are for sure better and more intuitive IDEs, but they come and go.

Emacs runs everywhere and stays.

I customized it to my needs, it's actually not an IDE but an IDE construction set.

Update

In hindsight, modal editing in vi style might be more appropriate for mobile keyboards. 🤔

So I will probably learn it, and take the extra step to activate vim emulation inside Emacs ;)