iPhone screen so large I can’t select anything

Three things to try (test after each attempt):

1. A forced restart of your iPhone as per these instructions:--> Force restart iPhone
2. Double tap on the screen using three fingers
3. Ask Siri (if enabled): "Hey Siri, turn off Zoom"

Regards

Giulio

if it's frozen try Force restart iPhone - Apple Support

if you want to unzoom try If your Home Screen icons are magnified on your iPhone, iPad, or iPod touch - Apple Support