How do i limit the amount of space Photos takes up?

I have an icloud subscription that is nowhere near full but when I try to take a picture or film a video the storage on my iPhone is always full because photos only removes backed up images when I’m low on space, so I can never record for more than like three minutes. Is there anyone who knows how to set a limit? My photos app takes 20gb but I’d rather it take around 10, and when I try to change it my only options are to download everything to my phone or to “optimize” space by removing old photos when until I’ve got like 1gb of free space. Thanks.