Deleting iPhone photos

It is not possible if you use iCloud Photos on your phone. The service is a syncing service not a backup service, so all the photos will be available on all your devices. You do have the option to turn on "Optimize Storage" in your Photos settings to reduce the amount of space your photos take on your iPhone. With this setting turned on, only the low quality versions of the photos will stay on your device until you need them for printing or viewing in a larger format. This is all done automatically. More information about this setting can be found here:

Manage your photo storage - Apple Support

Hello. It will be amazing if you could tell me the reason why you are trying to do this :) Then i can give you a solution to solve that!

But for now I believe that even if you un-sync from the cloud, it might be deleted as the photos are already stored on the cloud. There is more information about iCloud Photos. You can read more about this on Set up and use iCloud Photos - Apple Support.

I hope this helps!