I tried to make it responsive because I knew a lot of people would visit the site on their phone. In my testing, gameplay works on mobile...without an on-screen keyboard. When that keyboard pops up on the screen, there isn't much room for anything else.
If you think it's something other than your on-screen keyboard that's messing it up, feel free to link a screenshot and tell me your device, browser, etc so I can look into it.
I'm using the same setup. There were several pages to click through before the timed text editing challenge. Two pages showed the text to edit in a static form before the timed challenge.