I'm thinking of blocking a boys number from my daughters phone
Why would you block her friend?
It is summertime and he is sending dirty messages to my daughter. She can't handle that.
Talk to her about the messages instead of blocking the friend. She will not trust you as much if you go through her phone and just block someone.
We told her not to text boys and she still does what she wants. It's just a phase.
It will help if you acknowledge that she does it and set some boundaries. She will be doing it behind your back, may as well have some rules in place.