Are you planning to make the game UI mobile friendly? As it is this is kinda unplayable on phone unfortunately. Regardless, the concept seems pretty cool!
it's a scaling issue. Players can manually change initial-scale on line 6 from 1 to a smaller value. I think there's a way to set it to dynamically adjust based off screen ratios but idk how that works. Great start! Can't wait to see how things develop.
Download a code editor, change initial-scale on line 6 in the .html file from 1 to a smaller value. .6 looks best to me but may vary depending on the phone.