While I agree with what most of yall are saying and I think Calderon is a much better triangle offense fit than Jameer Nelson or some other point guards on the market, I think that just because Phil has never coached an elite PG (and won championships anyway), doesnt mean he could not win with an elite PG if he brought one in. I think it would be no different than it would with a player like Melo, as long as he buys in and learns the offensive system Phil/Fisher would make it work.
When Phil and Tex Winter first tried to install the triangle offense in Chicago as assistant coaches, Doug Collins refused (and exiled Winter in the process), because he thought the system was too team oriented for the NBA, and especially would never work around a superstar talent like Michael Jordan. But When Phil took over as head coach, he obviously made it work and it made MJ more of a team player.
Then in Los Angeles it was thought the Lakers would have trouble utilizing the system around Shaq because the Bulls never relied on a center to score when they ran the triangle. But once again Phil obviously made it work.
I think having a great PG here would be similar to the Shaq situation in LA. Phil never relied on a center for offense in Chicago because he simply did not have the personnel to do so. But once he was given a chance to coach a dominant offensive center like Shaq, he tweaked the system in order to utilize Shaq's dominance and get the ball to him in one-on-one positions in the low post.
I think that just because Phil has never relied on a great point guard to flourish in his system does not mean he would not be able to do so. I think the bigger problem is more the lack of elite point guards on the open market. The best realistic option is probably Rondo, and even he is a long shot and not a great triangle fit because of his lack of shooting ability.
Phil likes his point guards to possess certain specific qualities over others (such as bigger guards over smaller, good shooters over point guards who need to control the ball alot and drive the lane to be effective, etc.) and I think Phil's skill set preferences work much more in a player like Calderon's favor over Shane Larkin's, but do I think it is a little bit of a myth that Phil would not be able to utilize the skill set of an elite PG if he had the opportunity to do so.