How to check the storage on your iPhone, iPad, and iPod touch - Apple Support
From the above link...Other: Non-removable mobile assets, like Siri voices, fonts, dictionaries, non-removable logs and caches, Spotlight index, and system data, such as Keychain and CloudKit Database. Cached files can't be deleted by the system.
A high amount of Other could mean data corruption...you might want to backup your phone and restore it before you run out of space and could be in worse trouble.
While you think about that quickly try deleting photos, videos, apps, etc. to regain some space.
Restore your iPhone, iPad, or iPod to factory settings - Apple Support