How can I free up space in my iPhone?

My iPhone’s storage is full. I have a 5s and iOS 11.2.6 My Mac is synced up to my phone. So with that in mind I want to transfer all my photos to my Mac, and have no pictures on my phone, and my Mac have all of them saved. I am not sure on how to do that without losing the pictures, because currently they both have all the my pictures, and if I want to delete the pics on my phone, then all of them get deleted on my Mac too.