I mainly use HH on my computer, but every now and then I only have a phone available. However, iOS at least has a hugely annoying problem with focusing on the input field, like this:
Is there any chance this could be improved? Additionally, the font size on iOS is way too large, and often results in overflow for 3+ characters.
I’ll file a ticket for improving scroll behavior and the font size. The font size we can definitely fix, but as the link indicates the scroll thing might be beyond our control (though we will try the solutions therein). I myself plan to start using iOS for reviews here and there so we can dogfood it a bit more heavily (we usually use desktop ourselves). Thanks for letting us know.
As an aside, one cool feature I’ve thought about adding would be for the questions/reviews/progress to “sync” in real time across all browser sessions. That way one can start on the desktop and continue on the phone and go back to the desktop seamlessly. This can be done currently in a partial manner by just refreshing the quiz page whenever the device is switched, but I think it can be even more seamless. Yet another thing in our endless backlog. 
Edit: I also verified that this scroll behavior is also present on Android (i.e., Mobile Chrome).
We’ve fixed both of these issues today. Attached is the new scroll behavior on my iPhone SE.
Thanks again for the report.
Wow! Night and day difference. Works absolutely perfectly on my iPhone 13 Pro.