I used to have a problem with this. I could go meetings back to back without uttering a word. I found that the best way to overcome this was to ease into being vocally present in the room by saying small things right away. It could be small talk or some irrelevant comment before the meeting started, and then try to maintain that momentum. That way I didn’t have to break my own silence and speaking up when it really mattered to me got a lot easier.