He was the guy who brought the first legit 3-4 to the NFL (originally with the Chargers, but later very successfully with the Oilers). That shit the Dolphins were running was a gimmick and the Fairbanks style is a soft as f*ck defense except when Lawrence Taylor was making it work. He brought a system that was better than any other 3-4 until Lebeau and Mora/Sidwell/Capers independently developed the zone blitz in different locations. He was a real Xs and Os man despite his weirdness.
Even then it could be argued that the 3-4 that was in place in New Orleans when Mora took over as head coach was partly built by Phillips and the Zone Blitz wrinkle they added was the finishing touch.