Deleting Photos from iPhone without deleting from the iCloud

If iCloud Photos is enabled, deleting photos anywhere will delete those photos everywhere.

You can optimize local storage on your iPhone, which will cache (some) photos locally, and will keep the photo library in iCloud. But again, don’t delete any photos you want to keep.

… Set up and use iCloud Photos - Apple Support

… Manage your photo and video storage - Apple Support

Here’s a good description of optimizing your storage:

Things to Consider before using Optimise … - Apple Community

"Deleting Photos from iPhone without deleting from the iCloud: How can you remove photos from iPad or iPhone without having it permanently removed from iCloud? What is the benefit of cloud storage?"

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About Deleting Photos:

If these are uploaded to iCloud then deleting them from your device will not remove them from iCloud. So, enable Photos in iCloud Settings. The benefit of iCloud storage is backup you your device's, and having a location to access your files, rather than having to carry them about on a flash drive in your pocket.

On the iPhone:

1. Click: Settings
2. Tap: your Name (top item)
3. Tap: iCloud
4. Tap: Photos (so that it is green)