Iphone8
When I turn my phone sideways or upside down, the screen no longer moves.
iPhone XS
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When I turn my phone sideways or upside down, the screen no longer moves.
iPhone XS
See this:--> If the screen doesn't rotate on your iPhone, iPad, or iPod touch - Apple Support
If you still can't rotate it, since it is still under warranty, have it inspected at an Apple Store.
Regards
Giulio
Make sure the screen orientation is not locked.
Look under Settings.
Iphone8