The first part, about the house rules, sounds bad but ultimately it's their house and their rules. Unless it's preventing you from going to school (I was confused by that part) then there isn't much you can do other than try to get them to see your point of view as well. A lot of parents are scared that their children are going to be in trouble, especially because of changing technology that they feel gives kids a new way of getting in trouble that they can't keep tabs on. If you're not going to be using your phone at night anyway, other than the principle of it then fighting to keep it in your room will just stress you out unnecessarily. Sometimes parents have rules that don't make much sense and other that do but we can't understand until later.
As to your parents calling you fat and getting angry at you if you go home with less than a 100% perfect score, that's incredibly unhealthy. Pressuring you to get a 100 score instead of 95 isn't going to do anything. I've never met anyone who got a 100 in every single test and exam they've taken no matter how hard they studied.
To me it sounds like your parents are afraid that you'll get in trouble and that this will be worse for you later in life as well as reflect badly on them as parents. Their fear that you'll get fat or get a 95 in a test sounds a lot like they're very insecure, too.
Have you tried calmly discussing this with them? Sit them down, don't get angry, try to explain your point of view and find some kind of compromise. Pick your battles too. There's no point fighting about a phone you wouldn't be using at those hours when something like calling you fat is much worse.
I don't understand why you say that therapy isn't going to help. I think it could help a lot. You can explain to your therapist what you're going through and how you feel. If it's a good therapist then the therapist will see that some of these things are actually being harmful to you. Then your therapist might offer to talk to your parents for you if you agree. This could be very helpful as your parents may have an easier time listening to another adult, and one whose authority they acknowledge. They may dismiss your complaints as a teenager's complaints but they might be more willing to listen to a professional.
I also recommend talking to someone at school if you can, like a teacher or counsellor, especially if your parents rule is preventing you from attending your classes. If you can find someone who is understanding enough and on your side, then that person might be able to explain to your parents why their standards of getting a 100 instead of a 95 are unrealistic and how this can even be worse for you in the long run.
It sounds like your parents are so caught up in trying to do everything right that they've forgotten that human beings aren't perfect and that some things are unreasonable and even hurtful. If they were concerned about your health they wouldn't be calling you fat, they would be providing you with healthy meals and teaching you about healthy habits instead, maybe even seeing a nutritionist to assess what your dietary needs are. If they were concerned about your scholarly success, they'd also be more focused on motivating you to do your best and only get angry if you had obviously slacked off and failed due to laziness.
This sounds like a tough situation to be in and I hope things change for the better!
