Phil Mickelson was already making headlines on Tuesday morning at the 2018 Masters when he showed up to play a practice round with Tiger Woods, which is practically unheard of in the careers of these two great golfers with 19 major championships between them.
However, Mickelson also drew attention on Tuesday at Augusta National for what he was wearing to play with Woods. Phil Mickelson is wearing a button-down dress shirt to play golf. It's embroidered with sponsor logos, so it's not like he just picked up a dress shirt at the local JCPenney before heading over to Augusta National this morning. It's done on purpose.
The shirt appears to be made by Mizzen + Main, which makes button-down shirts with performance fabrics to help the shirt breath and not feel stuffy like a cotton button-down dress shirt. It also appears to be a seersucker shirt, which the company sells for $115 each.
Mizzen + Main makes other clothing as well, including polo shirts which use similar four-way stretch performance fabrics.