Phone sex with my boyfriend

My boyfriend and I recently became long distance, we will be apart for about a year. He wants to have phone sex, which i don’t mind, but he wants to me to masturbate on FaceTime with him and i feel weird about it. I feel awkward and when i tell him i feel weird and don’t want to do it, i feel like he gets upset, but he doesn’t show it. I feel like he will get mad if i never do it. Any suggestions on how to become more comfortable with doing it on FaceTime?