Bennett graduated from Texas A&M University with a degree in education in 1978, and was a second-team All-Southwest Conference defensive end as a senior in 1977. He began his coaching career at A&M in 1979 as a part-time defensive ends coach. Since then, he has also held coaching positions at Texas Christian University (1982, 1997), Iowa State University (1983–1986), Purdue (1987–1990), Louisiana State University (1991–1994), a second stint at Texas A&M (1995–1996), the University of Oklahoma (1998) and Kansas State University (1999-2001).
During his first season at Kansas State, in 1999, he was nominated for National Assistant Coach of the Year. During his years as an assistant coach he has coached many stand out players, including Mark Simoneau and [[Terence Newman
On October 28, 2007, SMU athletic director Steve Orsini fired Bennett. Orsini notified Bennett that he would be dismissed after the Mustangs' last game on November 24, 2007 against the University of Memphis.
University of Pittsburgh head coach Dave Wannstedt named Bennett his defensive coordinator on February 4, 2008. After Wannstedt's resignation in December 2010, he announced on January 3, 2011 that he was declining to coach in the BBVA Compass Bowl. Bennett was promoted to interim head coach of the team and lead the Panthers to a 27–10 victory of Kentucky.
On January 7, 2011, it was announced that Phil Bennett would join the Baylor Bears as defensive coordinator, replacing Brian Norwood who accepted the position of associate head coach for Baylor.
On May 26, 2016, it was announced that Baylor was firing Art Briles as head coach, and that Bennett was a candidate to serve as interim head coach, but declined the proposition and the Bears hired Jim Grobe to replace the fired Art Briles
On August 11, 1999, Bennett's 41-year-old wife, Nancy, was killed by lightning while she was jogging near their home in Manhattan, Kansas. The story of the Bennetts' relationship and the subsequent death of Nancy was the subject of a 1999 feature article in Sports Illustrated, as well as College Gameday on December 6, 2014. Bennett has a son, Sam, who is engaged to Stephanie Kaufmann, and is expected to be married in the summer of 2017. He also has a daughter, Maddie who followed in her mother's footsteps and became a nurse. Bennett remarried a long time friend Julie White Bennett in 2005 and has two stepdaughters; Katie and Megan.