I guess you are interpreting the answer of the officer the wrong way. Minors do have rights. Plenty of them. But using a phone to contact people their legal guardian does not approve, or to consume media their legal guardian does not approve, is usually not a right minors have. And to make those restrictions stick, your mother took your phone away. Ask for it on your 18th birthday.
But when one of you has called the police on a family situation like this, both of you have a problem that goes way beyond property rights. Do you have an adult you can talk to? A teacher? An uncle or aunt? A coach? Try talking to them. If they all side with your mother, consider that she might be right and you are wrong. But often both sides talk themselves into a corner, and a neutral viewpoint helps.
If you are truly desperate about your situation, call Child Protective Services. But that could backfire if they believe your mother, and make the family situation worse. Taking a phone away is not neglect or abuse.