Phillips was born at the Subic Bay Naval Station in the Philippines, the son of Lucita Umayam Arañas and Gerald Amon Upchurch, a Marine C-130 crew chief. His father was an American of Scottish-Irish and one-quarter Cherokee descent, and his mother, a native of Candelaria, Zambales, is Filipina, with distant Chinese, Japanese, Hawaiian, and Spanish ancestry.
Phillips was named after Marine legend Leland "Lou" Diamond. After his father died, he took his stepfather's surname "Phillips" as his own. He was raised in Texas, where he attended Flour Bluff High School in Corpus Christi, graduating in 1980. He graduated from the University of Texas at Arlington with a BFA in Drama.
During the making of the movie Trespasses, he met Julie Cypher, an assistant director. They married on September 17, 1987 and divorced on August 5, 1990.
He later married Penthouse model and television extra Kelly Phillips, with whom he has three daughters: twins Grace and Isabella, born in October 1997, and Lili, born in September 1999. They all reside with their mother. The two separated in 2004. Their divorce was finalized in July 2007. He began dating makeup artist Yvonne Boismier in 2004. They married in August 2007. Their daughter, Indigo, was born in October 2007.
|1987||Ritchie Valens||La Bamba||Movie.|
|1988||Angel David Guzman||Stand and Deliver||Movie, nominated for a Golden Globe.|
|2009 - 2011||Colonel David Telford||Stargate Universe||20 Episodes.|
|2012 - 2017||Henry Standing Bear||Longmire||63 Episodes.|
|2015||Saúl Guerrero||Blindspot||Guest Roles, 2 Episodes.|
|2017||Jeff Romero||Brooklyn Nine-Nine||2 Episodes.|