The French Rugby Union has formally told the WRU of the players' May 21 release and informed the two relevant clubs in France.
Wales caretaker head coach Rob Howley has praised the decision as an example of northern hemisphere co-operation during international preparations.
The May 21 date falls outside the formal IRB date of release for players involved in international duty and release is either contracted by individual Unions or discretionary.
Howley said: "This is fantastic news for us as it means Mike and James will be fully involved in the complete preparation programme we have in place.
"They are both experienced international players but it is still a huge advantage to have them working within our environment from day one.
"We are extremely grateful to the French Rugby Union and the individual clubs involved for taking this step.
"It is a gesture which will undoubtedly benefit the players and I know they will want to thank their individual clubs for helping them fulfil their international commitments with Wales.
"It is an example of northern hemisphere rugby working in unity for the benefit of our players and the game in general.
"We are all aware of the difficulties we can encounter when Welsh qualified players are based outside Wales, but this decision shows there are opportunities for us to realise mutual benefits."
Both the former Ospreys players left Wales for France this year with Phillips joining Bayonne and Hook linking up with Perpignan.
Yesterday they were both named in the 38-man training squad to prepare to face the Barbarians at the Millennium Stadium on Saturday, June 2 before embarking for Australia.
Clermont Auvergne full back Lee Byrne was not selected as he is still likely to be involved in domestic competition in France until the date the tour party departs.