But still, after going through all the trouble to get the component, why would he trust Philip enough to give it back to him? Even if they were both getting on the sub and planning to go together, I don't see why he'd trust Philip with it.
Chang wanted to make sure the Chinese would get the component even if Jack captured him. Additionally, he knew that Philip would need the component or the Chinese wouldn't let him on the sub. He had no reason not to trust Philip, because the sub was Philip's only way out of the situation and only way to get to China to start his new life.