The appointment of Phillips comes after Nigel Davies was named as attack coach, with Robin McBryde being put in charge of the forwards and Neil Jenkins taking responsibility as kicking coach as his backroom staff for the two-Test trip to Argentina next month.
"Rowland will be a valuable asset to the team and completes our complement of young coaches accompanying the squad on tour," said Jenkins.
"It is important for us to have a team of specialists covering all the different coaching areas and defence was the one outstanding appointment.
"There was a piece in the jigsaw still missing and that was a defence coach.
"The immediate need is the tour to Argentina. I need a defence coach out there and Rowland was more than happy to take on the role.
"Rowland is part of the Wales Under-18 coaching group. I think his track record and reputation stands for itself."
Phillips was capped 10 times at union between 1987 and 1989 and hit the headlines in Wales after taking Neath to back-to-back Welsh Premiership titles in 2005 and 2006.
And his rugby league background - he had a spell with Warrington in the 1990s - has helped him develop his defence coaching.
"Being an ambitious coach, like a lot of others are, to get this opportunity with the senior Wales set-up is huge," admitted Phillips.
"I had to take a bit of time to take it all in after Gareth spoke to me, but I'm really excited about it.
"As a player it was an honour to get the call to play for your country and this is the same as a coach.
"The opportunity to be involved with the senior Wales squad is an honour and I'm really excited about it. It was a huge surprise but an uplifting one.
"The appointment is just for the tour and that is going to be tough anyway. There is a lot of work to do before we go and during the tour.
"I don't think we are going to be looking too far beyond the tour. It's going to be a tough tour and it will be all hands on deck."