Turn the device when it makes sense
Landscape is not decoration — it changes readability.
When it is worth turning
The difference between playing on a phone in portrait and landscape is bigger than it looks. The grid gets bigger, the buttons sit further apart, and you mis-tap less.
When it is not worth it
Card games and simple scrolling ones work fine in portrait. Games with a wide board ask for landscape.
Note
On most phones, auto-rotation lives in the quick settings.