I certainly hope they go with a three man rotation, but you're really making an assumption. The Yankees haven't even officially committed to their game four starter, let alone their starters for the rest of the series.
Also, I think Charlie Manuel is making a huge mistake only having Lee pitch twice in the series. I understand that he has never gone on three days rest before, but, if it gets to a game seven, they likely pay dearly for this decision. In my opinion, you have to put the weight on the shoulders of your top players, and, for the Phillies, that's Cliff Lee.