McMahon missed out on the opportunity to win a Leinster Championship due to an injury earlier in the championship. Crokes defender O'Sullivan managed to gain a regular place in defence during his absence. McMahon made a substitutes appearance in the All-Ireland Senior Football Championship final against Kerry. He came on as a substitute for defender James McCarthy in a game that he and Dublin won by a scoreline of 1-12 to 1-11.
In November 2012 Philip was appointed Strength and Conditioning Coach at Shamrock Rovers.