Not sure if this helps for you but try to regulate your breathing a couple of times before picking up. Breathe in slow and deeply though your nose and out the mouth, and hold it like that for a couple of seconds. If they hang up before you can answer it's either not that important or they'll immediately call you back. It's even easier when you have to call someone because then you can really take your time to get into a mindset. Just take your time and don't rush it.