To make room for Romero, the Rockies designated right-hander Edgar Gonzalez for assignment on Monday.
Romero made 24 appearances for Philadelphia before being designated for assignment on June 16. He cleared waivers and signed minor league deals with Washington and then the New York Yankees before being released by New York on Aug. 8.
Gonzalez, who signed a minor league deal with Colorado in June, made one appearance after joining the Rockies earlier this month. He gave up two runs in two innings Sunday at St. Louis.