When you use the MakeCode editor on a mobile device, you may find that the micro:bit simulator (the micro:bit on the screen) has been replaced with a triangle `play` button.
This is because MakeCode has detected that you are using a smaller and less powerful device that a Desktop/Laptop PC and has switched to a 'light mode' which uses less CPU power. This mode disables the use of the simulator when the editor is loaded.
To enable the simulator, press on the grey 'play' button to load it.
If you no longer want to view the simulator. You can press on the 'stop' button to hide it:
And the play button to show it: