I have tons of space on my iCloud. My phone can’t download an app because it’s too full. What is the point of backing up my iPhone into iCloud if it doesn’t free up space on my phone?
iPhone 7, iOS 15
The point of backing up is that if your phone is lost, stolen, damaged, etc. you will be able to recover your data.
An iCloud Backup does nothing to free up space on your phone; however, syncing Photos via iCloud Photos can potentially free up space if you turn on the Optimize Storage option of iCloud Photos. See the "Free up space on your device" section of What's the difference between device storage and iCloud storage? - Apple Support
The point of backing up is that if your phone is lost, stolen, damaged, etc. you will be able to recover your data.
An iCloud Backup does nothing to free up space on your phone; however, syncing Photos via iCloud Photos can potentially free up space if you turn on the Optimize Storage option of iCloud Photos. See the "Free up space on your device" section of What's the difference between device storage and iCloud storage? - Apple Support
Once my iPhone is backed up to iCloud, how do I get space back on my iPhone?
