if I store photos in the cloud may I delete photos on my phone and MAC? Thus clearing up space.
If I store Photos in the cloud may I delete Photos on my Phone and Mac for more space?
No. iCloud Library its a syncing feature, not an off computer storage facility. Any change to the library on one of your devices, i.e. additions, edits, deletions, etc., will be reflected in the iCloud library and the other device.
If you want to store photos as a backup get an external drive an export the originals in the library to folders on the external drive. Then backup that drive along with your boot drive with Time Machine.