Phillips spent 10 minutes in the bin, but his powerful runs from quick-tap penalties kept the Blues on the front foot as they ran in three tries and restricted the Celtic League champions to three penalties.
Blues lock Deiniol Jones opened the scoring in the seventh minute with a rare try and young winger Chris Czekaj - who replaced All Black legend Jonah Lomu in the side - silenced the home crowd with a well-taken try in the corner as the game entered its second quarter. Centre Jamie Robinson found himself in acres of space and hurled out a pinpoint pass to give the teenaged Wales cap a simple run-in.
Phillips's high shot on Wales team-mate Jonathan Thomas earned him a 10-minute rest, but the Blues took a well-deserved 14-6 lead into the break.
The Blues' Nicky Robinson and former All Black fullback Adrian Cashmore traded penalty goals early in the second half, and Ospreys winger Richard Mustoe was yellow-carded for taking opposite number Craig Morgan out without the ball. Morgan had the last laugh with his side's third try as Ospreys fans began leaving the stadium.
Ospreys: Pens - S Connor 2, A Cashmore.
Blues: Tries - D Jones, C Czekaj, C Morgan; Pens - N Robinson 3; Cons - N Robinson 2
Halftime: Cardiff Blues 14-6
Yellow cards: M Phillips (Cardiff Blues), R Mustoe (Ospreys)
Referee: Phil Fear (Wales)