how to move photos/video OFF my iPhone and into iCloud. (not just duplicate)

I understand how to synch my photos, so there's a copy of my photos/videos in iCloud and on my iPhone. But how do I MOVE my photos/videos OFF my iPhone and into the cloud?

I keep running out of storage on my iPhone and I've paid for plenty of storage in iCloud. I don't see the "cloud" icon on my photos on my iPhone, which would indicate they're in the cloud and my iPhone is just showing a thumbnail of the photo with the ability to download to my iPhone if desired.