Scrum-half Phillips and back row cum lock Thomas are fully aware of the history of the fixture, as well as what it could mean to their hopes of securing a Play-Off spot.
Prior to the introduction of regional rugby in Wales in 2003, the rivalry between Neath or Swansea and Llanelli was always a talking point whenever fixtures were announced or cup draws were made.
Regional rugby may have brought Neath and Swansea together but the rivalry between the Ospreys and Scarlets is already beginning to match that intensity.
The two sides go head-to-head at the Liberty Stadium this weekend and, when you throw in the fact that the Ospreys have fallen outside the top four and the Scarlets are in real danger of missing out on the Heineken Cup, it could be a real humdinger of a clash.
"When the fixture list comes out in the summer, it's always one of the first that the players look for," said Thomas.
"There's a great rivalry there. It's something which comes historically from fixtures between Neath or Swansea and Llanelli in the old days.
"That brings with it a real passion from the fans. The fixture usually gets one of the biggest crowds of the season and that creates a special atmosphere.
"We played down there at Christmas and had the first sell-out at their new ground and, likewise, we've had some memorable games at the Liberty with a sell-out crowd as well.
"When you've got a big attendance, a passionate crowd and a big rivalry, it's one of those games that you want to be involved in as a player."
The Welsh regions have worked hard to create their own identity since their inception under former Welsh Rugby Union chief David Moffett.
Much has been done to bring people together but Thomas insists that this particular pre-regional rivalry is as much a part of the game as it ever was, and that can only be a good thing for players, coaches and spectators alike.
"We are only a young organisation really. We haven't been going seven years yet so we haven't really had much opportunity to create our own history or to build tradition," added Thomas.
"That comes with time, and will happen the longer we go on. These games against the Scarlets are the nearest we've got to tradition at the moment as they spill over from the pre-regional days. They provide us with a bit of tradition that as Ospreys we can take hold of.
"As a youngster, pre Ospreys, I was fortunate enough to be able to play in some big Swansea vs Llanelli games. I remember going across the Loughor Bridge on the bus to take on what was a very strong Llanelli side at the time as a very young player.
"They were always wonderful games to play in, and I think the rivalry between Neath and Llanelli was always strong as well. I think the Ospreys Scarlets derby is the one Welsh derby that remains that still has that needle in it."
That needle that Thomas speaks of is accompanied by the desire for bragging rights over fellow internationals, with the 27-year-old admitting that getting one over on mates adds a 'bit of extra bite'.
But if the Ospreys are to gain the upper hand when it comes to Welsh banter this season, team-mate Phillips knows they will have to improve on last weekend's disappointing showing at the Dragons.
A strong Ospreys side were comfortably beaten 28-20 at Rodney Parade and Phillips realises that improvements must be made this time around.
"We've had a good talk this week and it wasn't good enough against the Dragons," explained Phillips.
"We lacked a lot of passion and didn't rise to the occasion.
"They came at us in the contact area, spoiled our ball and were superb.
"They were just up for the game, far more aggressive than us. It's a simple game and they wanted it more.
"It's a massive game against the Scarlets and we have to show commitment and passion.
"I'm sure that will be there this week for a home game in front of a big crowd on a huge occasion."
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