Track messages or calls on my kid's smartphone?

Recently, I began to notice that my teenage daughter doesn't behave as usual. It seems to me that she is hiding something, and of course, it negatively affects our relations.

I would like to say right away that we have always trusted each other, but the problem is that she is clearly hiding something and acts suspiciously. Moreover, it's rather other children that I don't trust. That's because I understand the potential of the Internet and how it can be used. Here I am talking about online bullying which affects a very large number of girls and women. today

I know that she spends a lot of time with the phone and often talks with someone in her room.

I understand that this may remind the plot of a black mirror, but so far, the solution that I am considering is to get access to her phone to check her calls or messages. I understand that she is unlikely to talk to me herself, so I want to influence this situation myself and so it promptly.

Maybe someone knows some services or applications (it would be more convenient) that would provide me with an access to her phone?

I think many parents are preoccupied with these pigs, in fact.