I would like to flag/star email when swiping left. Is it possible with gmail account in iOS mail app?
You can only change what a right swipe does in iOS. You can change what the middle option on a left swipe is, but a full left swipe will still be delete/archive.
Check out settings -> mail, contacts and calendar -> swipe options.
Swiping left gives you three options, with the middle option being customizable.
You cannot change the left swipe to have only one option, unfortunately - it is built into iOS.
The middle option of the left swipe can be set to
Flag if you so choose, leaving you with a swipe-tap motion.