The 58-year-old actor said her "I, Tonya" co-star reminds her of Hepburn as neither of them wanted to be labelled as "the beautiful young thing".
"I just kept thinking of Katharine Hepburn when I looked at her (Robbie). Katharine put together 'The Philadelphia Story' because she wasn't getting the parts that she wanted, and that's what Margot did," Janney told The Hollywood Reporter.
"She was going to be typecast as this beautiful young thing, and she wanted to find interesting roles for herself and for other women, so she took the bull by the horns and she formed this company," she added.