Iphone only using email to send messages?

My iPhone is sending my messages by my email instead of my phone number. It won't let me select my phone number. I tried turning iMessage off and turning my phone off then turning it back on and turning back on iMessage but no luck. Why is it only letting me use my email and how can I fix it?

Did you update your phone?
I did and my phone is doing exactly the same and my texts aren't showing up on my phone, only on computer (which has iMessage). Hopefully the next update will help. I tried a hard reboot (hold power button and home key down) but that didn't work.