I would guess a phone is way too small for side by side diffs, and a simple `git diff` would probably be more useful. If you want better syntax highlighting you could setup bat[0] as your difftool. If you insist on a side-by-side view (neo)vim has a diff mode with the -d flag. It is also possible to setup as the difftool that git uses.

[0]: https://github.com/sharkdp/bat

Heh, many years ago I actually started writing a dedicated diff viewer app for Android [0] that specifically had synchronized horizontal scrolling between the two sides, and I remember finding it relatively usable in landscape, and I’m sure modern phones with larger and higher density screens would be even better.

But yeah, you definitely need a native experience to make side by side diffs viable on mobile.

[0] https://github.com/scottbez1/superdiff — I wish I had recorded some videos of the app back then. My code review workflow back then eventually stopped including diff attachments on code review emails, so I abandoned development on it.