If you haven’t played Sudoku before, think of it as a crosswords puzzle, but with numbers. Simple versions of Sudoku can run on any phone, and it can be an incredibly immersive game once you get past the initial learning curve. If you need help figuring out the rules, Gogetgame.com has a useful guide on how to play Sudoku that’ll help you get started.
Classic card games in general are easy on your phone’s hardware, and few of them are as universally enjoyed as Solitaire is. Simple versions of Solitaire can run on any phone, and every phone should have it.
One thing all these games have in common is that you don’t even need to download them in order to play. They can all be played straight from a web browser, both on PCs and on mobile.