Kids Dad Took My Phone

I have an iPhone 12 that I gave to my daughter to use a year ago. It’s my back up phone in case anything happens to my current phone. Her dad put the phone under his service contract. He bought her a new phone and refuses to give me my phone back. He insists that it’s a gift and he is going to sell it even tho it was never explicitly stated that the phone was a gift. He said it was our daughter’s decision to sell the phone so she could afford AppleCare and he would support her decision. I told him I would help pay for the AppleCare just give me my phone back. He refused and sold it on FB marketplace. Is this considered theft or am I SOL? EDIT: he told me I would have to buy the phone back from him also. Sounds like extortion to me but maybe I’m wrong I’m just a layman.