No storage on iPhone but can't delete because of iCloud
I have an iPhone 5s 16 GB and a 21.5" iMac 1TB. I use the Photos app on both. Recently I subscribed to 1 TB of iCloud storage as a way to sync my Photos library (about 300 GB) between my devices and have access to my photos from anywhere.
My storage is full on my iPhone and when I imported my photos to the Photos app on my iMac it didn't give me the option to delete the photos from my iPhone. When I attempted to delete the photo's off my phone I got the warning message saying "This photo will be deleted from your iCloud Photo Library on all your devices".
My question is how can I free up storage on my iPhone but keep my photos on my iCloud Library and iMac? I love the ability to view and edit my photos from all my devices but need to be able to continue to take pictures with my iPhone.
iMac, iOS 9.2.1