If I recall correctly, the provisional becomes the ball in play at the moment you play a stroke from beyond where the original ball was lost. You can actually hit the provisional more than once and then still find and have to play the original ball.
But in Phil's case since the provisional was a good drive in the fairway, he would have needed to sprint to the provisional and play a stroke with it (thereby causing it to become the ball in play) before "the guy" found his original ball. Phil's not much of a sprinter though.
I've had the experience before of hitting a ball into the woods, playing a provisional which also is mishit into trouble, then taking a couple of strokes to advance the provisional a couple hundred yards out in the fairway. Since only at that point has my provisional passed the likely spot of the original ball it's worth taking a quick look before playing that next shot, hoping to find the original and be able to play it. Then again, by that point I'm so fried I'm going to make a snowman or worse no matter what happens!