Can the family Sharing 200GB storage be shared for backups of my everyone's iPhones?

We purchased the 200GB plan thinking that that storage space can be used to backup multiple phones. But when I try to backup to the iCloud, it says not enough storage and indicates that I only have 5G of storage, some of which is already used. I was expecting to see 150GB of storage available.

If that space is sharable, how do you do it?