inflight wifi login problem

On a recent American Airlines flight, I was able to get to the T-Mobile page for the free session. I entered my phone and then the Captcha code, and the next screen asked if I wanted the 1-hour free or the full session. I made my choice, but when it wanted me to confirm, I couldn't scroll the screen up to be able to click the "confirm" button. Whenever I could get it to scroll up, when I lifted my finger to tap the button, the info snapped back down, so that the button was just below the screen view on my phone. I've never had this problem before. I don't know if this is a T-Mobile, an internet provider, or Apple iPhone issue.