On anything with a touchscreen the controls appear on their own. The left of the screen walks — put a thumb down anywhere and the stick appears under it — and anywhere to the right of that looks about. Both work at once.
Down the right-hand side: E to use what you are standing at, ! to swing, O to hold your shield up, ^ to jump, X to change tool, Q to build, and M for the menu. A thumb on a button presses the button rather than starting a walk. The Chat button sits in the bottom-left corner.
The prim tools are a mouse job. Walking,
looking, fighting, gathering, talking, the quests and the menus all work with
two thumbs. Shaping prims means dragging a gizmo handle at pixel precision, and
that is not something a thumb does well — you can reach the tools on a
phone, but a build worth keeping wants a mouse.