Please how can I increase the brightness of my phone

If increasing the brightness doesn't work try the other things shown in this link...

Adjust the screen brightness and color on iPhone - Apple ...Official Apple Support › guide › iphone › ios

On your Home Screen, swipe up from the bottom of the screen (Or swipe down from the top right on newer iPhone models)

You will see a bar with a sun on it, next to the sound

Now you can set the preferred brightness