My dad wants to get me a phone? Can my mom take it away?

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My parents were never married, they had me when they were around 17 years old. My father, just recently followed through with parenting meetings and paid for lawyers and such to set up for visitation rights for me and my brother. My mom and step dad are very strict about my phone. No password, can't delete texts, no Snapchat, no Instagram, no Twitter, literally nothing that people my age has, I can have. They always hold it against me... If I don't do this or that I will get it taken away and its gotten so far that I have been grounded from it since November. The only time I get it is when I babysit. For example: if I babysit for an hour, I get to have my phone for an hour. Simply because they don't want to pay me for babysitting if they don't have to, so, not having my phone since November, I take the deal. So, my step mom gets to upgrade her iPhone 5 to an iPhone 5c sometime this week and she said that she is just going to give me her iPhone 5 opening a new line for me, paying for it. Which ultimately brings me to my question. If my dad gets me a phone and he pays for it, can my mom legally take it away? The law is really weird with stuff like this. Like, I know that my mom can't punish me for something I do over there and vis versa. I'm 15. My dad and step mom believe that I should be able to have some privacy, whereas my step dad and mom do not think I should have any. I don't want to hide it from her that I have it, but I also want to have it.