This means he will now be leading Xbox, Xbox Live, and other related creative teams including Xbox Music, Xbox Video and Microsoft Studios.
Here’s a quote from the email by Microsoft CEO Satya Nadella:
Phil will continue his close partnership with Yusuf Mehdi, who leads business strategy and marketing for Xbox, George Peckham, who heads up third-party partnerships and Mike Angiulo, who will continue leading Xbox hardware.
Phil Spencer also wrote a post on his new position over on Xbox Wire. Apparently, we will “hear much more as we head into E3″. More details available on Engadget.