It is possible to play the web version on mobile! After launching the game, inside of the Pico8 interface, there is a small rectangular button which is the "PAUSE" button. After pressing it, the game opens a menu that allows you select an option called "Joystick: OFF". Pressing on that option turns it ON and makes the movement of the directional buttons be mapped to the movement of the cursor. The (X) button is your main interaction button and the (O) button opens and closes the inventory. Hope this helps!