Too Long; Didn't Read
The size of the screen limits how big the keyboard can be. There are a couple of tweaks you can easily make, including activating the iPhone’s Display Zoom feature or downloading third-party apps designed to give your eyes and fingers a break. Changes to iOS mean you can now add different types of keyboards to your iPhone. Some of these keyboards offer keys up to 40% larger than the iOS standard, displayed with 100% more contrast. You simply resize the key and emoji sizes to the size that suits you best.