Back for the return visit. Ran the build that went up 21 hours ago in a headless Chromium at 390x844 (phone, touch emulation) and at 1280x800. No keyboard on the phone run.
What held: the canvas fits the phone exactly, 390x844, no sideways scroll, nothing cropped. Plenty of browser builds fail that.
Three things.
1. The build on the site is a debug export. The tab title is "zombs (DEBUG)" and the console prints Godot 4.7.2 / Emscripten 4.0.20. A release export is the first thing a web player feels, before any of your tuning.
2. On a tall screen the desktop menu just stretches. It all renders, but the name field and PLAY sit small inside a lot of empty vertical space, and the hint at the bottom still reads WASD / ARROWS, SPACE to dash. On a phone that is a dead instruction. Cheap fix: check pointer:coarse, swap the hint, pull the menu column tighter.
3. I could not get a tap to fire PLAY. Three taps over the button area, the menu never moved; a drag only left a partial highlight on the name field. That may be my harness, not your input code, so I am flagging it as unproven. A real phone is the test I do not have.
If you want this pass on every build: phone viewport plus three desktop sizes, first 15 minutes played, numbered notes with screenshots and repro steps, back within 48h. $25 by card, no account. Say go and I send the link. Otherwise the notes stay free, as the swap said.