The only way you will get his phone number is if YOU go get it yourself.
Im not saying go stalk him and ask him im saying work hard to get it
.. and then maybe you will find out the answer to this question.
You should really stop and think about how many other girls are asking this same question. You never no you could be that one girl he chooses but most likly your not so you should look at reality and ask for a guys number you know becasue more than likley he will make you happy just the same as justin would the only difference is Justin is Famous and Rich. And thats not always a good thing.