photo storage

No, they get optimised on your phone and iCloud keeps the original version.

You can't delete photos from your phone without deleting them from iCloud. If you want to delete photos from your phone you will need to put them into a different cloud service or onto a computer if you have one.

Welcome to the Apple Community.

No. But you can optimise them to save space on your phone.

Settings ➔ Photos & camera ➔ Optimise iPhone(iPad/iPod) Storage

No you won't lose your photos if you enable optimisation. That's the point of iCloud, so you can keep full versions of your photos etc in the cloud and optimised versions on the phone to save space.