It’s awful, I actually search the discussion looking for this very post and disappointed to find there’s no work around. The APP whether on an iPhone or iPad the text field set for communication is about 2% of the entire displayed page.
So much information is displayed clearly yet where you are designated to type is extremely small, only a few lines. Worse yet, there’s no preview so you either have to scroll up and down and hope you have things right or press send and watch your jibber jabber post to your guest.
Airbnb is not setting us up for the most professional communication or success. They encourage host and guest to use the app that make it difficult to do so. The simplest fix is a larger typing field or have the full-time web developers allow a more modular and user specific view where you can choose the size of each field based on preference.