Free up storage space
How do I delete the photos from my phone but still save on my iCloud
iPhone 13 Pro
Question marked as
You don't, iCloud is a syncing service. If you delete them from your phone, they will be deleted on the iCloud as well.
Here are some helpful articles that can guide you on how to free up storage space on your phone.
How to check the storage on your iPhone and iPad - Apple Support
Manage your photo and video storage - Apple Support
Clear Other storage on your iPhone or iPad - Apple Support