Can I get my phone back

You should be able to get the phone you purchased back from the other parent, but I expect the other parent does not agree your child should have a phone during their time with him/her. While that may not be what you want, it may be difficult to get an agreement on this point without taking the dispute to the other party through a judge or mediator.  Often parents hold phones as a punishment, or because they do not agree it is age appropriate for a child to have a phone, or to prevent or limit their access to the internet or social media.  Depending on how your custody judgment reads, one or more of these reasons may be a valid parenting concern that need to be addressed. I would need more facts to be able to understand the real issue underlying this problem, but it should be something that can be worked out.