Delete other storage off iPhone
How do you delete storage off iPhone categorized as “other?” My iPhone says storage is low and I deleted some videos off my camera roll but it still shows my storage at capacity.
Here is Apple's version of what to do about the "Other" storage:
How to check the storage on your iPhone, iPad, and iPod touch - Apple Support
and here is a user's tip:
What is "Other" and What Can I Do About It?
Generally, short of a third-party solution, about the only thing you can do (if you are really serious) is to restore your device from a backup or, failing that, restore your device as new:
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Restore your iPhone, iPad, or iPod to factory settings - Apple Support