Wales axe Hook, Phillips and Hibbard
The announcement was made by Welsh coach Warren Gatland on Thursday.
Flyhalf Hook, capped 78 times, scrumhalf Phillips, who has made 94 international appearances, and 38-cap hooker Richard Hibbard failed to make the cut after Gatland trimmed his squad from 46 players to 38.
Jack Dixon, Rhys Patchell, Nicky Smith, Rory Thornton and Dan Baker are the other players who will return to their respective clubs and regions.
"It's been a difficult task reducing the squad down and deciding who will meet up with us again on Monday," Gatland said in a statement released by the Welsh Rugby Union.
"There will be disappointment from the players, but it's important to stress that the door is not closed. We name our final Rugby World Cup squad on August 31st and a lot can happen between now and then.
"As a squad we will now meet up again on Monday to continuing preparing for Ireland away, which is just over a fortnight away."
Hook, Phillips and Hibbard all started in Wales's 35-21 defeat by Ireland at Cardiff's Millennium Stadium last Saturday.
Wales tackle Ireland again in Dublin on August 29 before playing Italy in Cardiff on September 5 as they gear up for the World Cup.
They open their World Cup campaign against Uruguay in Cardiff on September 20 and will also face hosts England, Australia and Fiji in Pool A.
Wales squad:
Forwards: Scott Andrews, Rob Evans, Tomas Francis, Paul James, Aaron Jarvis, Gethin Jenkins, Samson Lee, Scott Baldwin, Kristian Dacey, Ken Owens, Jake Ball, Luke Charteris, Bradley Davies, Dominic Day, Alun Wyn Jones, Taulupe Faletau, James King, Dan Lydiate, Ross Moriarty, Justin Tipuric, Sam Warburton.
Backs: Gareth Davies, Rhys Webb, Lloyd Williams, Gareth Anscombe, Dan Biggar, Rhys Priestland, Cory Allen, Tyler Morgan, Jamie Roberts, Scott Williams, Hallam Amos, Alex Cuthbert, Leigh Halfpenny, Matthew Morgan, George North, Eli Walker, Liam Williams.
Agence France-Presse
