[Pikamander2]

It seems to work fine on a scaled down desktop browser though, and the existing game UI should be suitable enough to fit on a standard phone screen, even if the text is a bit hard to read.

I think OP just made a small mistake with some of the CSS/JS that handles resizing the game window on mobile viewports. In some cases the buttons are outside of the game, and in some cases the game window isn't using up the full screen real estate.