Stefanski was officially named the Browns' new head coach Monday, coming over from the Minnesota Vikings where he served as their offensive coordinator. He received a five-year contract, a source told ESPN's Adam Schefter.
Phillips spent the last three seasons with the Los Angeles Rams, where he was the top defensive assistant for another young head coach in Sean McVay. Phillips' contract wasn't renewed following the 2019 campaign.
The Browns ranked 21st in total defense this season under coordinator Steve Wilks.
Phillips, 72, has coached for 11 teams over his NFL career, beginning with the Houston Oilers in 1976. He won Super Bowl 50 with the Denver Broncos as their defensive coordinator in February 2016.