Phone storage full with large system data

This is the only way to reduce it

Back up the phone, Erase all content & settings, Set up the phone again, restoring the backup.

Resources:

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

Erasing:  Erase your iphone to factory settings

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

Then add back credit cards, sign back into accounts etc.

AlWeir wrote:

I would check what you have store on your iPhone starting with photos, then email and texts. Off load the photos to a computer or another storage medium. Get rid of email you don't need that might have attachments of photos and anything else that is taking up room.

Everytime you update the iPhone the OS is taking up more and more space and leaving you with less storage memory for your own personal stuff. Apple's answer for this was why they created iCloud and have users pay for it.

They would need to empty recently deleted in order to remove it from System Data caches. Attachments and Photos should not be in System Data unless deleted.

IOS updates may take up more iOS but not usually System Data

This delinquent system data is caused by poorly written apps such as Games, and beta testing.

The backup, erase and restore is the most thorough and should bring system data down to about 6GB

I would check what you have store on your iPhone starting with photos, then email and texts. Off load the photos to a computer or another storage medium. Get rid of email you don't need that might have attachments of photos and anything else that is taking up room.

Everytime you update the iPhone the OS is taking up more and more space and leaving you with less storage memory for your own personal stuff. Apple's answer for this was why they created iCloud and have users pay for it.