I don't buy Phil's reasoning for the raise, but the move is probably the best among tough alternatives. The rainbow and paired flop doesn't help a drawing hand, so Unbluffable is either way ahead of a bluff, or way behind to a pair of Kings or trip 5s. (Given the pre-flop weakness on Phil's part, it would make kings less likely.)

If Phil just check-calls with nothing on the board to draw to, that looks suspicious, and he might not get any more chips from Unbluffable. If Phil reraises all-in, that'll show maximum strength and chase Unbluffable away. Phil's move to reraise the minimum continues the guise that he's just representing a hand, and makes the bluff read more plausible.

It's bad luck for Phil that the two-outer hit, but it's not necessarily bad play by the opponent either.