This means your iPhone only stay in the current portrait mode view and when you rotate your iPhone, it doesn’t move into landscape mode as it should. You may see a lock icon in the top-right of your screen.
There are a few actions that may fix your landscape mode issue depending on your phone and iOS version. Here you go:
- For iOS 6, Go to Settings->General->Use Side Switch and make sure it’s not on lock.
- Reset your iPhone by holding down the home and power buttons together until it turns off and on.
- For iOS 7, swipe up from bottom of home screen top to reveal the screen lock control and unlock.
That’s it. Follow each step until your iPhone is not locked any more for landscape mode. No iPhone experts need to apply here.