I forget what the number is (you can find it on partner hub), but yes I have called twice. Once nothing happened right away (both the DM and SM were fired within a few months because many people called, though, I think mine was one of the first calls so it wasnt taken too seriously). The second time, my call was taken seriously and dealt with by the DM within a week. You can choose to be anonymous depending on the situation, so if possible do that if it would make you more comfortable. I also have phone anxiety, so I always write down a few notes of what I want to say before I make any phone call. I hope that helps!!