I'm no fan of Justin Bieber as a musician or as a person, but if you throw your phone on stage during a concert you can't complain about what happens to it!
I do feel kind of sorry for performers in this instance. I heard it explained by the guys from One Direction, which has just as many fangirls as Justin Bieber, that the audience doesn't realize that they can't really see them during a concert because of the lights, so it often they won't see things being thrown from the audience until it hits them in the face.
They kind of joked about it and told a story about how someone threw a walkie-talkie on stage and talked to them at the other end of it. Both they and the interviewer commented how that was very cleaver, but then one of the guys added "But don't throw it...that hurts!"