O how I remember this. That thud in your gut when you cannot get ahold of them. One thing I did learn was that I had to stop my mind from running away with me every single time. I automatically assumed the most horrible situations each time. To be fair, most of them were not what I imagined. Were they sometimes, sure. Were they the other times, nope.
I learned there is no point in worrying myself to death, that no matter what happened I would handle it. I still feel that way even though we are divorcing. We still have kids together and I still have fears.
Also, distraction. When I had fears I set myself into being busy, and it's a sort of busy that occupies my mind. Throw myself into work. Go out with a friend and do something. Talk to a support person.
You are not there. It cannot hurt you and can only affect you if you let it.
Big Hugs.