I think it depends on the person, so I'm not sure anyone's going to be able to give you a definite answer, unfortunately. However, based on my own experience with a fear of making phone calls (don't think the level of anxiety I have qualifies for an actual disorder, but it's still not much fun ), generally the reason I get scared is that I'm not sure what I'm going to be expected to say, or what questions I might get asked. So if someone who's made the same, or a similar, phone call can go through what should happen, then it can give me the courage to make the call because I know roughly what to expect.

So, if the reason your friend is scared to leave his room is because he doesn't know what scenarios he's going to meet, maybe you could go through the most likely ones with him and suggest what he could do, to give him a sort of plan?

Not sure I've been much help, but good luck - I hope you can find something that works!