Laura Mackenzie Phillips (born November 10, 1959) is an American actress and singer best known for her roles in American Graffiti and as rebellious teenager Julie Cooper Horvath on the sitcom One Day at a Time.

Born in Alexandria, Virginia, Mackenzie Phillips is the daughter of John Phillips, lead singer of the The Mamas & the Papas, and his first wife, Susan Adams. She is the sister of Jeffrey Phillips and a half-sister of Tamerlane Phillips, actress Bijou Phillips and singer Chynna Phillips.

At age twelve, Phillips formed a band with three of her classmates and was spotted by a casting agent during one of their performances. She was given an audition for a role in the 1973 hit film American Graffiti, which she won.