Do you bring a bluetooth keyboard with you or program with two thumbs?
Also, using two thumbs can be more awkward if you have big hands.
The awkwardness of phone coding isnt the typing of text (wherein most people rely on decent prediction rather than precise typing), it's the use of symbols.
Not every programming languages require a lot of symbols. Like Python, Go, OCaml etc. For me writing many symbols is awkward even on a physical keyboard.
Not if you're using a Swype-style keyboard.