How to remove other in storage

If you’re running iOS 14 or iOS 15, Other is the stuff that really can’t be removed.

Here is how Apple defines Other storage: 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.

It’s where (for instance) apps using iCloud keep their data stored locally. If you reset the device, the apps and the rest will then incrementally re-download and rebuild and re-populate that Other storage and those caches.

Here are some ways to offload the contents:

How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

Manage your photo and video storage - Apple Support

If this is a 16 GB iPhone, or if this is an iPhone with storage capacity inadequate for your current usage, then this iPhone will never not need storage management, unfortunately. Off-loading and “optimizing” (as described in links above) can help, but it’ll usually be ongoing work to continue to fit within the limits of the iPhone.

And no, there are no memory upgrades, short of a newer (used, refurb) or new iPhone.