LeBron took umbrage with Jackson describing his posse as a posse.
Until LeBron brought it up, I would never have thought of "posse" as a racially-charged term. In fact, after my high school reunion I was saying things like "I didn't get that much time to talk to everyone because I mostly hung with my posse." To me, the term means "a group of people who like to hang out together." I've never even heard of any group of black guys being called a posse, although I wouldn't have excluded it in my definition, but I guess I may not read the right sources or talk to the right people that would enable me to identify the link between "black" and "posse." I suppose LeBron is in a better position to make this association.
Now if Phil had said "homies," that would have made me cringe because I associate that one with black urban slang, and even though it's not derogatory, per se, it always sounds creepy and pejorative when old white dudes try to emulate the slang of other groups.