Hi Brian, that expanding sounds kind of weird. It must be something the web browser has decided to do.

It's not unusual for a web browser to allow enlarging the text type-in field which is called a "textarea" element, but I would think it should push other stuff down further rather than covering them up.

If you tap somewhere outside the field like somewhere on the background of the page outside it, does that do anything?

Sometimes textareas are sizable by dragging in their lower right corner, that might be worth a try.

Also are you maybe able to hit a "Tab" key? That should put focus onto the "Post" button and when it has focus pushing enter should trigger it.

You also could try a different browser like Firefox:
https://support.mozilla.org/en-US/kb/will-firefox-work-my-mobile-device

- Michael