system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If my cell phone camera supposedly shoots 4k video, why does the "4k" video it shoots look so bad?
gpt
One possible reason is sensor size.  The larger the sensor, the better the image.  The Sony a7iii can record 4k, and the physical dimensions of it's image sensor is 35mm x 28mm, while the image sensor in your phone is somewhere around 5mm x 5mm.  The physical dimensions of the image sensor can make a big difference in image quality.