Another super useful trick when typing on your iPhone is the zoom option. A lot of times you have to go back and edit something you typed, but trying to tap with your finger between two characters is half the time impossible and the cursor ends up somewhere else.
All you have to do is press and hold your finger over the text and then a magnifier glass will pop up. Slide your finger left or right to move one character left or right at a time. This makes editing text a hundred times easier!
"iPhone Tip – Zoom into Position"
Reference : online-tech-tips.com