First, keep in mind that Holliday is eligible for free agency following the 2009 season. In other words, the Phillies might have been exactly where they are now in having a key member of their offense potentially headed off elsewhere through free agency. The only difference is that they would have been without key players that they would have had to give up to get Holliday for one season in Philly.
It's worth noting too, that Holliday isn't quite the hitter away from the Rocky Mountains that he is at home - or at least what was his home. In his career, Holliday is a career .357 hitter at home and drops to a .280 mark on the road. Plus, he has hit 66% of his 128 career home runs in Colorado. Holliday has never played in Oakland, but in Colorado, he hit one home run every 16.1 at bats. One sad note for Phillies fans who were dreaming of having him in town is that he hit one home run every 13.3 at bats in Philly, even topping his Colorado percentages.
The Rockies repeatedly brought up names that the Phillies didn't want to part with, starting with Shane Victorino and moving on to Jayson Werth. The Phillies figure on Victorino and Werth as key pieces of their team and have no intention of moving them - especially Victorino - in a deal that wouldn't give them a long-term player. As good as Holliday is and as much as the Phillies would have liked to be introducing him to the Philadelphia media, the Phillies are just as happy to have Victorino and Werth stay in town.
The A's gave up their closer, Huston Street, and two younger players to get Holliday. The Phillies wouldn't have had to give up their closer, but the next best thing. Without Victorino or Werth as a centerpiece to the deal, the Rockies would have had to have someone like Ryan Madson to replace Street in the deal. While his name never directly came up, there is no likelihood that the Phillies would have liked the idea of sending Madson off to the thin air of Colorado.
Oakland pitcher Greg Smith would have likely had to been played by J.A. Happ, or possibly, and much more to the Phillies liking, Kyle Kendrick. The Rockies insist that Smith was the key to the deal and could be the only one to stick with the Rockies. Street and outfielder Carlos Gonzalez are already on the trade market out of Colorado. With Colorado being so insistent on Smith, they might have been just as insistent on having Happ as part of the deal, even if it meant dropping demands for Madson.
The Phillies don't have a Carlos Gonzalez clone - a young outfield prospect with power - and would have had to substitute their best outfield prospect Greg Golson in his place. The Rockies also might have asked for infielder Jason Donald in place of Gonzalez.
When you add it all up and do the analysis, it's likely the Rockies would have centered their request to the Phillies around J.A. Happ. From there, they might have lowered their expectations on the other players in the deal and settled for Golson and possibly Chad Durbin as the other parts of the deal. From the Phillies standpoint, the best possible deal they might have been able to swing would have been Kendrick, Golson and Durbin, but it's unlikely that would have been enough. Something more like Kendrick, Donald and Durbin, might have tempted the Rockies, but it's likely that wouldn't have been enough, either.
Any way that the Phillies would have shaped the deal, it wasn't likely they were going to get Holliday, unless they were willing to part with the likes of Victorino, Werth or Madson as the main part of the trade.
While the Phillies could have used Matt Holliday, sometimes the best deals are the ones that you don't make.