On the face of it, I would say she is being unreasonable. She has three 'sporty' kids and one who doesn't like sport but she refuses to acknowledge that personality difference.
Sending you to camps all the time seems to be an effort to get you out from under her feet. But only for a few days at a time. Some parents (the well off ones) ship their kids off to boarding schools and only see their children in school holidays. They can then work long hours or live the high life while knowing their kids are looked after. It doesn't mean they don't love their children.
Going to camps is a good way to meet others of your own age and make new friends. If you've been spending days indoors, on your phone all the time, maybe she wants you to be more outgoing? Do more exercise, too?
Taking your phone away is either because the texts you send to her have annoyed her (in which case you will have to ask her the reason why) or she wants to prevent you getting/keeping boyfriends or prevent you from posting things on the internet which will cause legal action or get her/your father fired and so on. Not deliberately but by being clumsy. Even bright people can behave thoughlessly but what you write on the internet is both permanent and easy to search.
If you wait a few days and google "my mom sends me to tennis camp", you should be able to find this thread.
The 'dietary supplement' is puzzling. Have you ever seen the packet they come out of? Are they vitamins, diet pills, medication or what?
Your siblings get different treatment simply because they are older. Its easy to fall into the trap of believing "me too, I'm ready for that" when they get gifted something nice on account of being more mature than you are. Your parents can't buy four of everything all at once; they may need to save for another year to buy the next car, for the next oldest sibling and so on. You will get your turn.
At all times, just remember that whatever you do to annoy your mum, it is the fourth time she's been subjected to it. Firstborn probably gets away with it, as it everything is a new experience to them. Child 2 is "oh, this again", Child 3 is "oh no, not again", Child 4: they either roll with it or they lose their patience. It's not your fault that they've been through it before but it would be unreasonable of you to expect them to have the patience of a saint and put up with any old **** that you dish out.