A quick restart can often fix the issue. Try restarting your phone once and see if it helps.

Your phone's location can cause it to become stuck in either landscape or portrait mode. Try moving it to another spot and see if it works better.

Sometimes you may have accidentally set a setting that causes the phone to only work in either portrait or landscape mode. Double check your settings and adjust them accordingly.

Dust, dirt, and other particles can cause your phone's accelerometer to malfunction, preventing it from operating correctly in both orientations. Gently clean your phone and see if it fixes the issue.

If none of the above steps work, seek out technical support from a professional. A qualified technician can help diagnose and repair any deeper issues your phone might have.