Some smartphones run at a reduced resolution (as well as other settings affecting image quality) as a pre-set default to try and save the battery life - despite being capable of playing back images at higher quality.

You’d likely have a better chance of learning to how to reduce the blacks appearing washed out on your phone checking on the phone manufacturers forum - or a similar tech-orientated forum (maybe check youtube etc?) for that specific model or range of smartphone.

Good luck with it.