Who ordered the hit on Tony and why?
I see three possibilities. They likeliest being that Butchie gave the order because the manner in which Phil's hit went down (in front of his family) caused too much unrest in his own family and possibly even with the other New York families. Phil was a jerk but he also did 20 years in jail without ratting anyone out, so it's reasonable to see people getting angry over such a brutal hit.
The second likeliest possibility is that Butchie was a snake who never intended to honor his deal with Tony.
The least likely possibility is that it was ordered by Carmine Jr, possibly for the same reasons as I gave for Butchie in scenario 1. Maybe he saw an opportunity to blame Phil's hit on Tony and Butchie, kill both and take over the family that his father once ruled. Carmine also had some joint construction deals with Tony that he might have just taken completely for himself afterward.