Phone screen test

Use edge-to-edge colors, then rule out the protector and software.

Short answer

On a phone, dust under a screen protector, overlays, camera cutouts, OLED retention, and physical pixel defects can look similar. A short manual color sequence narrows the possibilities.

Open phone screen check Open quick colors

What to look for

Clean the screen and inspect the protector first.
Browser controls may remain visible on iOS; the screen-filling color view still uses the available browser area.
Disable color filters, extra-dim modes, and screen overlays while checking.
Use another camera to photograph a physical defect.

Use this order

Rotate to the orientation where the mark is easiest to inspect.
Run black and white.
Run RGB manually.
Take and view a screenshot on another display.
Use the phone maker’s built-in diagnostic/support flow if the mark remains.