You can absolutely use a phone or tablet! That said, make sure to quickly read the following requirements.
iPhone and iPad
First, you'll need to make sure you use Safari browser. Second, your version of iOS needs to be at least 11.2, unfortunately older versions do not work with our newer technology.
Use Google Chrome browser, and make sure it's updated! As long as you do that, you should have smooth sailing.
All Devices - Swipe Left to Access Chat!
You can still see the chat messages your teacher sends, even on mobile devices. If you don't see chat on your screen, just swipe left to get to it.