My family sharing option cannot be selected. It’s greyed out. How do I fix this?

i need to set up family sharing as my daughter is going to start to use my old iPhone. I’ve never done this before so I’m error, we trying to connect her phone to my iCloud so that I could back up her photos, I did not do my research and because this stuff dies not come to me intuitively, I started to connected her iPhone straight to my Apple ID. So long story short, after research the major error- that I lost the ability on my iPhone to set it up via family sharing Bc it was defaulting to my daughters phone. I reset her phone now thinking it would default back to my phone but it’s still grey out. Please help. I would very grateful for any guidance.