Even if he did give the phone to Ben right there, and called them up, by going to the radio tower and shutting off the message. Would it matter? Jack would still kick the crap out Ben. Thinking they made a deal. But i'm guessing Ben knew that Jack wouldn't give him the phone. Ben would let the bad guys come, just to let Jack know that they are dealing with the real baddies. And which sets Jack up in the flash-forward.