My IPhone storage

Upgrade to current iOS 13.6.1, if your iPhone supports that, and if you have enough free space for the upgrade.

Otherwise... Back up, reset, and restore.

How to back up your iPhone, iPad, and iPod touch - Apple Support

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

If all of the storage is being eaten up by “other” data, try updating to iOS 13.6.1 if you haven’t already done so.

Clear Other storage on your iPhone or iPad - Apple Support