The Cowboys placed Phillips (wrist) on injured reserve Wednesday, Todd Archer of ESPN.com reports.
Phillips underwent wrist surgery last season while playing for the Bills, but it remains to be seen whether his current injury is related. He'll now be forced to miss at least Dallas' next four games, making Oct. 27 versus the 49ers the earliest possible return date. To help replace Jenkins, the Cowboys inked Carlos Watkins from the Commanders' practice squad.