Storage and iCloud storage

I'm paying 2,99€ each month for iCloud storage. I have only used 124/200 GB of it. My iPhone storage space however is full. The goal is to move something from my phone to iCloud, but I don't know what.

I have a lot of pictures, so thats why the red part, photos, is taking most of the storage space.

My questions are:

Why are the photos taking storage space also from my phone? Isn't it enough that it takes up space from iCloud? Am I doing something wrong, or is it unavoidable to have photos that don't take up storage space from the phone?

If I share pictures to a shared album, will they be removed if I remove them from my phone? Because if not, isn't it then the solution for having pictures available on your phone, that don't take storage space?