Moore dropped out of the film earlier this week after being hospitalized for what her publicists described as "exhaustion."
Steinem is not expected to figure prominently in the film, which features Amanda Seyfried as Linda Lovelace, the troubled star of the iconic porn film "Deep Throat." Peter Sarsgaard plays Lovelace's ex-husband, porn production manager Chuck Traynor; James Franco has a cameo as Hugh Hefner; and Hank Azaria is set to appear as Jerry Damiano, the director of "Deep Throat."
Parker will next be seen in "RIPD," a supernatural cop drama starring Ryan Reynolds, Jeff Bridges and Kevin Bacon.
For more on "Lovelace" and Moore's current struggles, click over to Us Weekly.
UPDATE: Whoops! Looks like Us had the wrong Parker. EW reports that Sarah Jessica Parker will replace Moore in "Lovelace."