Hi DexterNZ,
Welcome to Apple Support Communities! We're glad to look into this typing issue in the Mail app with you.
So that we understand completely, let us know exactly what's going on. It sounds like the email message you're typing is scrolled too far up, and you've got to scroll down to see the text as you type. Is this correct?
Is this only occurring in replies, or does it also happen if you start a new email?
Is the test of the message being obscured by some Mail app interface? Do you have a custom signature set up in Settings > Mail > Signature?
Have you had an opportunity to restart your device since noticing this behavior? If not, please do so now. A standard restart is best. Here's a guide with the recommended steps:
Restart your iPhone
If the issue persists, let us know which model of iPhone and version of iOS you've got. The version can be found under Settings > General > About.
Also, please let us know if you're experiencing similar behavior in any other apps. Also, is your iPhone set to display larger text under Settings > Display & Brightness > Text Size?
Have a great day!