As a true freshman at LSU in 2017, Phillips played in 12 games, recording 18 tackles.[5][6] As a sophomore in 2018, he started 11 of 12 games and finished the season with 87 tackles and a sack.[7] Phillips returned as a starter his junior year in 2019. Following a junior season where he led the team in tackles, Phillips announced that he would forgo his senior year and declared for the 2020 NFL draft.[8]
Phillips was drafted by the Cleveland Browns in the third round with the 97th overall pick of the 2020 NFL Draft.[11] The Browns previously acquired this selection from the Houston Texans by trading Duke Johnson to Houston. Phillips was placed on the reserve/COVID-19 list by the team on December 26, 2020,[12] and activated on December 31.[13]
On September 1, 2021, Phillips was placed on injured reserve with a biceps injury.[14] He was activated on December 11.[15]
Phillips entered the 2022 season as the backup middle linebacker behind Anthony Walker. He became the starter in Week 4 following an injury to Walker. He started the next four games before being placed on injured reserve on October 26, 2022, after suffering a pectoral injury in Week 7.[16]
On August 13, 2023, Phillips was placed on injured reserve.[17]
Houston Texans
On April 23, 2024, Phillips signed a one-year deal with the Houston Texans for $1.15 million.[18][19] He was released on August 27.[20]