making letters on keyboard bigger?

Hey guys, im making some enquiries on behalf of a friend. Firstly I know the majority of you guys here use VoiceOver as do I, hence why im so clueless about this. Basically, im trying to find out more about the magnification abilities of the iPhone. Specifically, I wondered if anyone knows of anyway that the keyboard can be enlarged on the iPhone while making shure that it is still all on the screen. For example, when you use Zoom, the keyboard does get magnified, but half of it disappears off the screen, so when typing, u have to kinda slide your finger along to get the othr half of the keyboard back onto the screen and the same when you want to move to the other side of the keyboard again. This poses a bit of a complication when trying to text, so was just wondering if you could give me some tips on how to magnify the keyboard while keeping it user friendly. Any apps, or anythng. Sorry for the long explanation, but this is not my area of expertise so I wanted to put all the information down. And any help would be most welcome Thanks:-)