delete pictures from my phone

How can I delete pictures from my phone without deleting them from my mac when I have iCloud photo library?

Simple answer. You can't.

The iCloud Photo Library is primarily a syncing system, designed to keep your photo library synced between subscribed devices. All edits, including deletions, are synced in real time between your Mac and your phone while the library is enabled.

It is not a hard drive in the sky and Apple currently has no cloud only storage options for photos.

For what you want to do, you need a different cloud based solution such as Dropbox, OneDrive, or Flicker.