Phillips is expected to return to his duties later this season.
The AFC South champion Texans own the NFL's top-ranked defensive unit under Phillips, who was hired in January after being fired as head coach of the Dallas Cowboys last November.
In the interim, linebackers coach Reggie Herring will call the defense. Herring coached the linebackers with Dallas from 2008-10 under Phillips.
Phillips' absence is another bump in the road for the Texans, who have battled through adversity to earn a playoff berth for the first time in franchise history.
The Texans have played a majority of the season without star wide receiver Andre Johnson because of hamstring issues, while the team has started three different quarterbacks after season-ending injuries to Matt Schaub and Matt Leinart.