He'd have to be willing to actually go in and file a formal complaint. They're not going to take an anonymous phone call even if the person gives a name. Do you have any idea how busy they would be running down every phone complaint? They probably have every crackpot around calling them, complaining about some BYU student.
The HC office is small, contrary to what some people apparently think, they don't have many students on their radar. They don't want to be going after anyone, they only do it if it's something that has to be done.