I am of the opinion that there is no such thing as a "right to privacy" regarding phones, social media, etc when it comes to kids. My kids know that I can and will look at their phones at any time for any reason. It's not that I don't trust them, it's that I know what's potentially out there, and it's my job as their mom to make sure they know how to use these things responsibly and intervene if they are not.
With that said, I'm so sorry this is happening. What he's saying is completely horrible and inappropriate. I agree with the suggestion to get her a new phone number if you possibly can, or at the very least block the communication between your DD and her father. Make sure you have EVERYTHING documented for your lawyer.