Jacoby isn't going anywhere. His value is very low right now because of the injury, and he's the kind of player that you generally don't trade-- but if you do trade him, you do it when his value is very high.
The Phillies want to get the most they can for Werth, and trade him out for someone like Roy Oswalt, because after Halladay and maybe Hamels, they don't have anyone to rely on in their rotation. So, I honestly think Werth is a good target because the Phillies are desperate enough, while there really is no good reason to trade a guy like Dejesus.