How to delete photos from iPhone, but not from cloud?

To free up space on my iPhone I'd like to remove all photos and 'start fresh'. They are currently backed up in iCloud. Is there a way to: a) delete them from the phone, but leaving them in the cloud, and b) re-enable the sync so that all new photos are saved to the cloud too? Point b is crucial as the solutions I found online involve three steps - with a major drawback: 1. disable the iCloud sync 2. delete all photos from phone (as sync is disabled, they will stay on iCloud) 3. the drawback: don't enable the sync ever again, otherwise the photos deleted from the phone will also be deleted from iCloud. (this sounds really stupid but don't want to risk it!)