Phil,
Are you talking about using the Casper strategy from the start, or using it after taking an unplayable and going back to the tee?
If you're going to play for a 3.5, what's wrong with taking an extra club and playing over the bunker on the right? If it comes off as planned you have a tough two putt but really can't do worse than a three putt. If you mishit it and put it in the right bunker, well, that may not be an easy up and down, but its still possible and again you won't do worse than 4 from there...
I don't think Phil's ego would ever allow him to deliberately play away from a green in regulation unless conditions were quite extreme, but playing away from a pin, that's acceptable.
Doug:
Phil had to think, and admitted as much in an interview, that that particular pin position on Sunday was one he was most fearful of, among the ones played in the tournament. After all, he went 3-2-3 on #4 on the first three days of the tourney.
If that's the case, I'm not sure why he didn't play short, other than either: a) he didn't think of it; or b) he didn't want to appear like a wimp.
Two pieces of evidence:
Here are the Sunday pin positions, per Dan Herrmann's thread:
Here is a link (posted somewhere on GCA recently) of Kevin Streelman's yardage/guide book to the Masters; it's one long take, but check out the very specific diagram of the 4th green, which appears to have a fairly severe false front (the narrow "tongue" of the green), a relatively flat mid-section that tilts from right to left, and an upper shelf along the entire backside.
http://www.golfwrx.com/forums/topic/464463-kevin-streelmans-yardage-book-from-the-2011-masters/Comparing the two (the Sunday pins, and Streelman's yardage book), it appears as if the Sunday pin for #4 was set just above the false front (looking at Streelman's book, the Sunday pin appears to be where the "7" is on the green diagram). My guess is that Mickelson was worried that landing a tee shot on the green to that pin would result in a downhill putt that risked rolling off the green. Streelman's book also suggests a severe falloff at the front of the green -- that is, the land fronting the green rises up to the false front. Video from the Masters website of Mickelson's play on Sunday on the 4th confirms this.
Given all that, it would seem the least troublesome place to put a shot -- given Mickelson's fear of that pin -- would be a simple shot to the lowest point of the area fronting the green, which would have left a very short and manageable uphill chip to a green that's not racing away from you -- in fact (given you're hitting into the false front), it's receptive.