Phones with 2 MP depth sensor

This is not the main sensor that records the photo: it does not image the frame directly but takes a supporting measurement for the main camera, and the result is used while the main frame is processed.

A depth sensor builds a distance map of the scene and helps portrait mode decide where the background begins and ends — it aims to reduce the errors made around hair and the edge of a spectacle frame. Its resolution is low because it produces distance, not an image; 2 MP here is not an indicator of quality.