Many people who enjoy Follies as I do only "get" either Sally or Phyllis. Not to say that they aren't smart enough to understand, but I think the understanding of both characters comes with age. Phyllis is the easier character to "get", I think. After all, Alexis stalked the stage in a stunning red dress, firing one liners and insults, and then is revealed in a leg showing dance number to finally let loose. Dorothy wore a frumpy pink dress and was given the more nuanced role - which she performed beautifully. She isn't particularly funny, she is the symbol of Follies - an older woman revisting her youth and attempting to regain what she used to have. She is a little weird and unstable - and her mad scene (following "Mornings") is difficult to understand to the casual viewer - and I believe only Collins truly understood it. By the time "Losing My Mind" comes around, everyone already knows that Sally has loved Ben for years, so it's less a shock as when Phyllis begins to show off her body.
Phyllis is easier to understand, and I think in 1971, people tended to recognize that.
"Sticks and stones, sister. Here, have a Valium." - Patti LuPone, a Memoir