Easy YDI. Your children are humans, and humans need privacy. Helicopter parenting teaches kids how to hide things from you, not good behavior. You love her, right? Then trust her to make good decisions and be there for her when she makes mistakes, and then MAYBE you'll earn her trust too.

Has your daughter actually done anything to merit a weekly thorough phone search like that? It'd be one thing if you had legitimate concerns based on past behaviour, but if she's always been honest and lacks any sort of seriously bad habits, this is really intrusive for no good reason. If anything, it'll just teach her that you can't be trusted with any information that might upset you, meaning she'll hide difficult or dangerous situations from you, rather than seek your help. Like, the very, very occasional random check might be reasonable, even for a generally good kid (to make sure you haven't completely missed something that actually might be concerning) - But weekly? That's just training her to make sure anything she doesn't want you to see isn't easily findable. In fact, I'd wager the group-joining and not hiding it might have even been to send you a message the next time you snooped through her phone.

You don't say!

never voted YDI faster in my life

Time to land that chopper. An occasional check to make sure she is staying out of trouble is reasonable. Unless she has given you reason not to trust her, or otherwise has a penchant for mischief, this is uncalled for. It will only lead to her not trusting you when she needs help.

YDI. The fact that you came here to talk about your WEEKLY INVASION OF YOUR CHILD'S PRIVACY with no context to indicate why you DISTRUST HER SO THOROUGHLY THAT YOU FEEL THIS IS NECESSARY, and expected anything less than her seeking help on how to cope with the CRIPPLING LIFELONE MENTAL AND EMOTIONAL DAMAGE you are causing her is what's most surprising here.

are you expecting sympathy? You need help

now you know how your terrible parenting makes her feel. instead of punishing her, take it to heart and make some changes. if this continues, you're not going to have a daughter after she's grown

Time to take the phone away. Kids don't need them and social media is toxic.

Did anybody consider that the OP could be the father and not the mother? If it is the mother then YDI.