What are my rights as a legal adult in my parents’ house?

Get your own phone. A TracPhone will cost very little.
Find a friend who needs a roommate, and a part time job.
You are more than old enough to get out of there, and it's clearly high time.
Treat it as an emergency, especially if they are accusing you of stealing.

To answer your original question, you have the same rights as a guest. You have the right to your own safety as long as you are on the property. You have the right to stay as long as you are welcome. It sounds as if your welcoming is cooling off, and your free rent is over. No one is going to prosecute them for a breach of privacy you have the ability to avoid.

You can move out, and you can get your own phone.

1 Do your parents own the phone? Then legal.
2. Their house, they can install cameras, legal.

Oh for god's sake, get your own phone and move out as soon as you can!

First, you are living in someone else's house.
That you are "trying to move out" is nice, but legally irrelevant.

1. Did your parent's proved you with the phone? Give it back and get your own.
2. You are 20 and you have a boyfriend and YES you HAVE doe things and will keep doing things. Your parents are not a stupid as you wish they were.

Legally they have done nothing wrong. It is THEIR house and you are just pretending to be an adult. Everyone reading this knows your next step is to move in with your boyfriend so you will go form your parent's child to his. The idea of growing up scares you so much yo will put it off as long as you can.

Legally, again, they have done nothing wrong.
If you do not like the rules then move out.
I am sure your boyfriend has a whole new set of them.

Get another phone. Don't tell them. Don't put the location tracking app on the new phone. When you want to go somewhere without them knowing where you are, don't bring the phone with the location tracking app.

Sorry but, their house, their rules. You are over 18. They can not stop you from moving out. Remove that app from your phone. Simple!

To answer your question; legally you are a tenant of the property regardless of your status as a bill payer. This mean your parents cannot evict you without proper notice and possibly seeking a court order to do so.

Your best bet would be to pack up and leave with no notice given. Legally, everything given to you is yours, so your parents cannot demand you leave behind things they have bought for you if that's an issue. If your phone is on their plan, then you should leave that behind and get a new phone. If your vehicle is titled to them, then leave that behind as well. You may use it to move, but then it should be returned to prevent legal complications.

If you have no options, like a friend or family member willing to take you in until you can find a stable residence, then you should seek public assistance. Just mention that your parents set up cameras to watch you in bed and they'll be looking to get you out of their right quick.

One step at a time. If you’re able to move out, you should be able to own your own phone too.

You have the right to be KICKED OUT.
Even rent paying tenants not related to the owners have less rights in the owner's residence than tenants renting a separate residence.
If you live under MY roof. you have all the privacy 'rights' I choose to grant you, and I reserve the right to CHANGE the rules on a whim.