He leaves the WRU with immediate effect following an agreement with Worcester to facilitate the early release from his contract with the Union.
Joe Lydon, WRU Head of Rugby Performance and Development said: "Phil is a highly experienced and accomplished coach and I am sure he will make a great success of his new venture.
"He leaves with all our best wishes and sincere gratitude for the excellent contribution he has made, both operationally and strategically within the WRU as National Academy Manager and as head coach to the Wales Under 20 squad during the last two seasons.
"I remain confident that the structures and systems Phil has helped put in place will benefit the game in Wales for years to come.
"Phil's departure provides an opportunity to take stock of the operations of the Performance and Development department, to review our programmes of delivery within the performance pathway and strategically plan how best we enhance all areas of delivery going forward."
Phil Davies said: "I want to thank the WRU and in particular Joe Lydon, Roger Lewis, David Pickering and the Board, along with all my colleagues at the National Centre of Excellence. I've been 100% committed to my roles here over the past two years, I've thoroughly enjoyed every minute and also learnt an immense amount.
"I'd also like to thank our partners within the Regions and the Premiership clubs who supported the National Academy concept and the Under 20 programmes we put into place.
"It has been a very difficult decision to leave the WRU but I have a huge passion for coaching and hope one day to coach Wales. With this in mind, I'm greatly appreciative of Worcester Warriors who have given me the opportunity to return to professional coaching, and to the WRU for considering and granting my request to do so."
WRU Group Chief Executive, Roger Lewis, said: "Phil leaves with our best wishes. While we are sad to see him go, I am pleased that we were able to conclude a swift and successful negotiation with Worcester Warriors for the release of Phil from his WRU contract."