The former Scarlets and Leeds boss, who has previously worked at the WRU as Wales Under-20s coach and National Academy Manager, again played a key role as Warriors secured Aviva Premiership status this season.
Charlie Little, Managing Director at Warriors, said: "We brought Phil in initially to be part of the team that took us back into the top-flight which he achieved in a difficult structure.
"The aim of this season was to consolidate in the Aviva Premiership and get ourselves in a strong position for recruitment. Again he successfully achieved all those ambitions.
"He has recruited very well in the forwards and he has had a very strong working relationship with Richard Hill and all the rugby staff.
"Phil is a proud Welshman and we realise this is a big opportunity for him. We have reached amicably terms of release with Cardiff Blues and we wish him well and thank him for everything he has done for the Warriors."
Head Coach Richard Hill said: "Phil has brought huge energy and massive enthusiasm to the role and we will all be sad to see him go.
"He has a terrific rapport with the players and brought them all together to improve them and make them better. He has really developed individuals.
"Phil has been extremely loyal to me and I have enjoyed working with him. He retains huge ambition in the game and the role at Cardiff Blues is a massive opportunity for him so we wish him well."