iCloud backup size is smaller than the data backed up
I'm planning to factory reset my iPhone Xr in order to start fresh but i want to keep some of the data that is currently on the phone like photos, messages and contacts. I figured that backing up these things to iCloud and then restoring them back after resetting the iphone would be the best solution but after backing up the iPhone to iCloud i noticed the backup size has two different values. On the backups page it says it’s 129.2gb but when i tap on it it says it has 138.69gb. Looking at the iCloud storage management diagram i believe the backup does indeed only take up 129.2gb as before backing up exactly 5gb of iCloud storage were being used. This is worrying because my photo library alone takes up 133.18gb. So i don’t know which of the sizes shown are correct and i am afraid that if i reset my iPhone and restore this backup i might lose data. I tried deleting the backup and backing up again but with the same result. I don’t have the iCloud Photo sync turned on. If someone could help me figure out what is happening i will be very thankful!
iPhone XR, iOS 16