Nervousness

So, I tend to mumble while talking to my boyfriend. I believe the mumbling comes from my nervousness, but the BF doesn’t help my nerves when after I’m done saying something says, “I’m sorry but I did not understand a single word you just said.” I literally scream into the pillow right next to me because I’m so frustrated. This makes our phone convos worse. (-_-)

I’d appreciate if anyone could tell me how to relax.