Children don't own property, their parents do. Anything you give to your child when in the other parent's care is effectively in that parent's control.
The phone does not have to be returned to your daughter, however it seems to me you have a valid claim to it.
If she refuses to give you the phone you could try small claims, but that would only get you a judgment for the value of the phone, not the phone itself.
Personally I would have the phone deactivated and not give her another. You can contact her through her home phone or mom's cell phone.
If mom is obstructing you from reasonable contact then you can address that in the family court.