Stephenson (back) was activated from the 10-day injured list Wednesday.
Stephenson had been sidelined by tightness in his upper back since late June, but he'll rejoin the Rockies after appearing in one rehab game. The 28-year-old has a 4.56 ERA, 1.56 WHIP and 27:13 K:BB across 23.2 innings this season.