Do what I do, keep the iPhone in your pocket, and use the app on an iPad Pro 12.9” with keyboard-cover.
The iPhone is a great device, but, truth be told, phones are too small for studying or getting work done. I use my phone for listening to Chinese Pod lessons as I do other things, Then find a comfortable spot to sit and type out my lessons/exercises on something with a keyboard. I got the newest generation iPad Pro a few months ago and find that with the keyboard it allows me to get some real work done: business, personal, and studying.
P.S. Congrats on getting the iPhone X so fast.