Small circular black spot on my iphone screen

Then make an appointment to have your iPhone examined:

Genius Bar Reservation and Apple Support Options - Apple

Contacting Apple Support directly may allow them to run remote diagnostics:

Contact - Official Apple Support

Try and force restart your iPhone to see if the problem persists

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the side button.