Let's please look at this with a rational head before the "Family over Everything" Dom Toretto bots come crawling out of the dark and slimy corners of Twitter at the slightest notion of insensitivity.
Phil Mickelson just sort of didn't want to go to the US Open. That's the opinion of Jason Smith, and his explanation is quite simple.
We've all just wanted to skip something before without explaining why. It doesn't make us bad people. There is a stupid event planned tomorrow night that I'm already not feeling up to. So you just tell someone you have a prior scheduling conflict and bail. This is a high school graduation for a private school that his daughter attends that has been on the schedule for a veeery long time. If he wants to make it a special moment, and that would be totally understandable, he is successfully doing so by provoking an article and a rant like this. She should feel very special.
That doesn't mean he also didn't really feel up to this. Jason Smith explains: