A handsome, multi-ethnic leading player, Phillips made his film debut as both actor and co-screenwriter with "Trespasses" (filmed in 1983, released in 1987), a crime melodrama set in Texas. He rose to prominence as doomed 1950s rock-and-roll star Ritchie Valens in "La Bamba" (1987). A charismatic and conscientious performer, he subsequently distinguished himself as gang member Angel in Ramon Menendez's high school drama, "Stand and Deliver" and was one of the titular "Young Guns" (both 1988). He has played cops ("Renegades" 1989), Latinos ("A Show of Force" 1990) and Native Americans ("The Dark Wind" 1991, "Shadow of the Wolf" 1992). He worked behind the camera as director and also starred in "Dangerous Touch" and "Sioux City" (both 1994).

In 1996, Phillips made his Broadway debut as the King of Siam in the acclaimed revival of Rodgers and Hammerstein's "The King & I". That same year, he was on the big screen as a soldier colleague of Meg Ryan's in "Courage Under Fire".