>>.I recall a horror film where some mass-killer dressed up like Santa Claus!
Christmas Evil? “He’ll Sleigh You”
aka Silent Night Deadly Night
http://en.wikipedia.org/wiki/Christmas_evil
>>Phil quickly realizes that his brother is the homicidal Santa he has heard announced on the news and proceeds to choke him unconscious.
Silent Night, Deadly Night! That’s the one! One of the holiday-themed slasher films. It’s been at least 25 years since I’ve seen it.