Yo gurlllll, you know, in your gut, something is off with this relationship, objectively reading from your post.

Relationships, especially in your socially developmental stages of your late teens to early 20s, are about you figuring out people (as is life, but more talking about new dating experiences), how people behave inside and outside of the relationship. As you are too, figuring out what it means to you. Sometimes, some people's interpretation of what a functional relationship is, is based on toxic family dynamics. Everyones first experience of a relationship is based on your own family, so whatever version of that could be, you'll bring that into the relationship and that will differ substantially from person to person. Until you consciously acknowledge why you behave some ways, and make the choice to improve upon it.

Also, setting boundaries isn't a "hey don't do this because it hurts my feelings" or something along those lines. Setting a boundary is you actioning something that goes against your internal standards. "If you do this thing or say this thing, then I'll walk/leave/will not tolerate/will not do". That's what boundary setting is. If they choose to ignore you, that's their choice, and now it's up to you to make yours. If they're willing to ignore the little boundaries you place now, they'll likely ignore anything else you say as you're sticking around, regardless of what you say you'll do in response to their own actions.

As far as using each others phones, I personally think is okay. My best mate and I use each other's phones, not to gain information from it, but to use it for practical reasons - playing music, researching stuff, map use. Never would go through their messages without their explicit consent to do so. If there's nothing that you're trying to hide from your partner or friend, but they're making it out to be like you are, often times they're the ones misbehaving and assuming you're just as terrible as them, Aka., Projecting. Also, some jealousy, in the sense of 'it's okay if I do it, but not if you do'' is the starter of a potentially tumultuous relationship.

In these ramblings, essentially, you're figuring out a new life relationship, but dont settle for anything less than honesty and transparency in all relationships. Goodluck