This is most likely a phone-processing artifact from HDR or a similar multi-frame mode. The phone quickly captures two or more images and combines them to improve detail in bright and dark areas. If someone moves between those exposures, the merged result can show a ghosted or doubled person.

That also fits with any blur in the photo: slight movement during the combined exposures can make subjects look smeared or duplicated.

To reduce the chance of this happening, keep subjects as still as possible, use good light, and if your phone allows it, try turning HDR or motion-enhancement features off for that shot.