Scrum half Phillips capped 94 times, and hooker Hibbard, who has 38 Wales caps, were part of the British and Irish Lions' successful tour of Australia in 2013.
Flyhalf Hook, who has played 78 tests, will also not get the chance to battle it out for a place in Gatland's final 31-man squad.
Less-experienced players Nicky Smith, Rory Thornton, Dan Baker, Rhys Patchell and Jack Dixon have all failed to make the cut.
"It's been a difficult task reducing the squad down and deciding who will meet up with us again on Monday," Gatland told the Welsh Rugby Union website (www.wru.co.uk).
"There will be disappointment from the players but its important to stress that the door is not closed.
"We name our final Rugby World Cup squad on Aug. 31 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."
Wales face hosts England, Australia, Uruguay and Fiji in Pool A at the World Cup, which begins on Sept. 18.
Wales training Squad:
Forwards: Scott Andrews (Cardiff Blues), Rob Evans (Scarlets), Tomas Francis (Exeter Chiefs), Paul James (Ospreys), Aaron Jarvis (Ospreys), Gethin Jenkins (Cardiff Blues), Samson Lee (Scarlets), Scott Baldwin (Ospreys), Kristian Dacey (Cardiff Blues), Ken Owens (Scarlets), Jake Ball (Scarlets), Luke Charteris (Racing Metro), Bradley Davies (Wasps), Dominic Day (Bath), Alun Wyn Jones (Ospreys), Taulupe Faletau (Newport Gwent Dragons), James King (Ospreys), Dan Lydiate (Ospreys), Ross Moriarty (Gloucester), Justin Tipuric (Ospreys), Sam Warburton (Cardiff Blues).
Backs: Gareth Davies (Scarlets), Rhys Webb (Ospreys), Lloyd Williams (Ospreys), Gareth Anscombe (Cardiff Blues), Dan Biggar (Ospreys), Rhys Priestland (Scarlets), Cory Allen (Cardiff Blues), Tyler Morgan (Newport Gwent Dragons), Jamie Roberts (Harlequins), Scott Williams (Scarlets Hallam Amos (Newport Gwent Dragons), Alex Cuthbert (Cardiff Blues), Leigh Halfpenny (Toulon), Matthew Morgan (Bristol), George North (Northampton Saints), Eli Walker (Ospreys), Liam Williams (Scarlets).
(Reporting By Michael Hann)
