Before we begin, I'll put forth that, of course, there's no such thing as an untradable player (except maybe Mike Trout), and that if the right offer comes along, you have to listen. That said, I don't think it's possible for the Phillies to get anything close to what Cliff Lee is "worth."
It's very difficult to determine what new information is coming out is legitimate, and what is the product of speculation gone awry. But I'm having a hard time imagining a scenario where trading Cliff Lee would be a net-positive for the Phillies organization, either in the short or long term.
1. Selling low. Cliff Lee has had famously bad fortune in 2012, and while at least some of it is his doing, the fact is that his peripheral stats are all solid to excellent, great indications of a possible rebound. Lee's FIP (3.41), xFIP (3.14), and SIERA (3.20) are all a good bit lower than his 3.95 ERA. His .319 BABIP and 13.5% HR/FB are both the worst of his career. Long story short, Lee has pitched in some rotten luck, and his good strikeout and walk numbers show that the ability is still there, and that adjustments can be made.
2. Leverage. Ruben Amaro, Jr. and the Phillies flat-out reek of desperation right now. While the Rangers, the prohibitive favorite trading partner, have pretty strong incentive to bring in some pitching help in light of the Angels' Zack Greinke deal, waiting until the offseason could clarify the situation a bit and reveal at least a few more viable buyers. And that, of course, is if you favor trading him at all...
3. Robbing Peter to pay Paul. "Pro trade" people suggest that freeing up the money from Lee's contract would enable to team to spend and improve the team elsewhere immediately. My problem with this, at least in theory, is that I have a hard time imagining spending the $87.5 million over three years left on Lee's deal in a way that would maximize the bang for the buck. At the risk of being glib, elite players like Lee are paid like elite players because (drum roll) they're elite.
I'm sympathetic to arguments regarding the luxury tax threshold, but reallocating the entirety of Lee's $24 million per season still leaves you at the threshold. It's just a matter of to whom the money goes.
4. Uncertainty in the rotation. With Roy Halladay's future as a Cy Young-caliber pitcher in substantial doubt, Lee, along with recently extended starter Cole Hamels, would at worst form a potent 1-2 punch at the top of the rotation. Whether or not Halladay returns to form, he is only under team control through 2013, and given the team's current financial situation, it's hard to imagine the Phillies re-upping him. If Lee departs, that leaves you in 2014 with Hamels, Vance Worley with bone chips in his elbow and questionable stamina/stuff, Kyle Kendrick, and a raft of B-C level prospects including Tyler Cloyd, Austin Hyatt, Trevor May, Jesse Biddle, Jon Pettibone, and Brody Colvin. You have to hope one or two of those guys pan out, because otherwise you're back on the market paying retail prices for average pitching talent.
5. Player relations. Good pal Ryan Petzar talked about it the other day over at the Complex. We all know how much money Lee famously "left on the table" to come back to Philadelphia. Trading Lee, whose family fell in love with the city during the postseason run in 2009, would once again pull the rug out from under a guy whose signing cemented the Phillies reputation as a destination team. Lee sees this, and players around the league see it too: If they'll trade Lee, they'll trade anybody.
Amaro and the Phillies braintrust could have a masterpiece brewing, but until then, I think Lee's presence on this team is more important than ever, and that unless they are completely blown away but some other team (this is possible), they simply need to ride it out with Lee.