That's a very different thing. End-to-end encryption stops Apple from reading messages on its own initiative, but if you discover that someone with a particular

That's a very different thing. End-to-end encryption stops Apple from reading messages on its own initiative, but if you discover that someone with a particular phone number is sending defamatory iMessages, Apple can still tell you who that person is. (Even the idea of a phone number being anonymous sounds kinda silly, even though it's no structurally different than a Facebook user ID.)