I think what I try to do is to get some form of noise out there during a pause, whether it's saying 'erm' or just something easier I can say. Once people realise that I want to speak they'll let me which is good. Weirdly on calls I find talking slowly helps too. Also if you can, switch on your webcam. I'm so much worse with calls than face to face and even though I don't like video calling too much it improves my confidence :)