Most of the time, your iPhone keeps dimming because Auto-Brightness is turned on. ... You'll have to turn off Auto-Brightness if your iPhone keeps dimming and you want it to stop. Open Settings and tap Accessibility -> Display & Text Size. Then, turn off the switch next to Auto-Brightness.

How do I stop my iPhone brightness from changing?

When auto-brightness is on, you'll notice that the brightness slider on your device moves according to changing light conditions. You can turn auto-brightness on or off in Settings > Accessibility > Display & Text Size. To reset the auto-brightness settings, turn off auto-brightness and then turn it back on.

Why is the brightness on my iPhone changing by itself?

Auto-Brightness, a feature introduced in iOS 11, aims to help users by adjusting the screen brightness through sensors that track how much light is around you. This means your iPhone's brightness automatically becomes brighter in brighter environments, and dimmer in darker ones. It also helps conserve battery life.