The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
A second try for Wales captain Ryan Jones five minutes into injury time denied the Scarlets a losing bonus point.
But though Phillips started, the Ospreys were without Shane Williams, sidelined with a shoulder problem.
The Scarlets were also without three of their big-name stars - Stephen Jones and club captain Simon Easterby (both rested) while Matthew Rees had a shoulder problem.
After a frenetic start the Scarlets opened the scoring in the third minute with a Rhys Priestland penalty after the Ospreys had erred offside.
The Scarlets doubled their lead seven minutes later with a second Priestland penalty from in front of the posts after referee Nigel Owens had to warn home lock Jonathan Thomas after tempers were lost.
The Ospreys also spurned the best try-scoring chance when Gavin Henson broke through up the left and on 30 minutes James Hook was off-target with a penalty goal shot from 30 metres away.
But five minutes later Hook found his range planting a penalty after Mark Jones and Regan King had collided trying to collect a Priestland cross-kick.
The Scarlets and Ospreys both suffered setbacks when Morgan Stoddart and Ryan Jones were both yellow-carded for not releasing the ball on the floor on 29 and 32 minutes respectively.
In first-half injury time Hook spurned a chance to level the scores, missing a penalty from close to his halfway line.
Seven minutes into the second half blood replacement Marty Holah crossed the line but the score was ruled out for a knock-on from Hook.
But on the hour mark the try stalemate was broken when Phillips skipped past two would-be tacklers to slide in by the posts for a converted try to give the Ospreys a 10-6 lead.
As the match entered its last 10 minutes Hook planted his second penalty to extend the Ospreys' advantage.
And at the death Ryan Jones went in under the posts for the second converted try.