Delete from iPhone but stay on icloud
I have
2 iphones
1 mac
all actived the iCloud photo library (on the mac is "download and keep originals", on two iPhones are "optimize iPhone storage")
when I plug my iPhone to the Mac and launch the "PHOTOS" app on the mac os, I can see my iPhone on the import section, once I click it, it recognize that all the photos on my iPhone already imported to my PHOTOS, that's very easy understand because when I took the photos by iPhone, it will automatically upload to iCloud, then my "PHOTOS" on mac will automatically download the photos from the iCloud.
The problem is, how can I release the space from my iPhone? because even the photos already imported to the iCloud, but it still storaged on my iPhone space, and if I delete it, it will delete it from all the icloud.