How do I remove gray box where text goes prior to sending it?
How do I get rid of the gray area?
iPhone 5c, iOS 9.0.1
A significant number of people are having that problem since iOS 9. One solution (at least a temporary one) is to quit Messages and then double-click the Home button to open the app switcher. In the app switcher find the Messages app and slide it up to remove it. Then close app switcher by clicking the Home button. That should solve the problem -- for a while at least.
Other solutions that are working for some (at least temporarily) include: restarting the phone, or going to Settings > Messages and toggle either the Show Subject Field or Character Count setting or turn Raise to Listen off.