If changing the font size overall on your phone did not change anything within the Gmail app and there is no font size setting in the app, Then there is not much else you can do. Did you check under accessibility? Normally changing the font size on your phone affects most everything else.....text size and so on.
When I was testing the Mailbox app, I could deal with its font sizes, but not that of the Gmail app. It's been a while since Ive used it, but unless we are given the option to increase the font size, I will NOT use it again. Besides, the native mail app is more than sufficient for my needs at this time.
I agree - it is completely unreadable. Too bad, because it's an otherwise decent app. I have searched hi and low, but the answer is NO, you cannot enlarge the text size. There are no settings for font size within the app and the Gmail app does not support "dynamic type", meaning the system settings for type size don't affect it and you can't pinch to zoom. As a new switchover from Android to iPhone, this is a big problem. Built in iOS mail is awful for gmail - it does not show sent mails in conversation view.
My best current solution is using the Outlook app. It works great with gmail (and other services). Only downside is that it doesn't do gmail labels, but it is very fast and easy to Move mail to folders corresponding to gmail labels.
If gmail fi