iOS will automatically change the orientation (portrait or landscape mode) of your screen, depending on how the device is being held. Here's how to lock the screen orientation of the iPhone or iPad.
iPhone - How to lock the screen rotation
iOS13
Swipe down from the top right corner.
Tap on the lock screen button as shown in the photo:
Your screen rotation should now be locked. To unlock it, you simply follow the above procedure and un-click the lock-screen button.
For Older iOS versions
Swipe your finger upward to display the Control Center.
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