He played college football for the Texas Longhorns and joined the San Diego Chargers as an undrafted free agent in 2014.

On November 2, 2014, Phillips made his professional regular season debut and recorded one tackle during a 37–0 loss at the Miami Dolphins in Week 9.

Phillips entered training camp slated as a backup safety and competed for a roster spot against Gordon Hill and Johnny Lowdermilk.

[11] Throughout training camp, Phillips competed for roster spot as a backup safety against Dexter McCoil, Darrell Stuckey, and Adrian MacDonald.

[12] Head coach Mike McCoy named Phillips the backup strong safety to begin the regular season, behind Jahleel Addae.

On October 2, 2016, Phillips recorded three combined tackles, a pass deflection, and made his first career interception during a 35–34 loss against the New Orleans Saints.

Phillips intercepted a pass attempt by Drew Brees, that was originally intended for wide receiver Michael Thomas, during the fourth quarter.

He finished the 2016 NFL season 38 combined tackles (25 solo), three pass deflections, and one interception in 14 games and five starts.

On September 11, 2017, in the season opener against the Denver Broncos on Monday Night Football, Phillips had an interception off of quarterback Trevor Siemian that helped set up a scoring drive for the Chargers.

[15] He played in 16 games with seven starts, recording a career-high 94 combined tackles, nine passes defensed, one interception, and a forced fumble.