I had the same issue, until my phone (iPhone 7 32GB Model A1778) suddenly turned off and then got into a loop starting up over and over again.
All of this after updating to ios 13.5.1, "other" went from 2~3GB to 13GB, then last time I was able to check it was 17GB, now I can't turn on my phone as it gets stuck in the loop.
Since I take a lot of care of my phone it is the only thing that comes to my mind.
The last comment of an url is helpless since it's a problem with the update which was made to prevent this problems "Description: A memory consumption issue was addressed with improved memory handling."
Guess is time to get a new phone.