DBs hold in tight coverage until they are caught. I imagine Vaughn decided he would hold like Kwhitt taught him to on each down to help win the game. Phillips was having a good game, has a size and speed advantage. And it was isolated coverage because they were bringing the blitz.
If he didn’t hold, Retzlaff throws the fade and Jojo catches the high point and if he breaks the tackle, it could go for big yardage.