Unfortunately neither the pilot nor the second episode feature the show's most popular character, Mother Dexter (Judith Lowry). The pilot does have Barbara Colby as Phyllis's boss and the ex-lover of her late husband Lars. (If you take into account everything we've heard about the unseen Lars, including the fact that he had an affair with Sue Ann and his sticking Phyllis with no insurance, you kind of have to conclude that he was the worst husband ever.) After three episodes, Colby was murdered; her part was re-cast, but all the same, the emphasis had to shift away from Phyllis's job and toward her life with her husband's family; finally she just changed jobs altogether.
The show collapsed in the second season when Lowry died; with the most popular supporting character gone and with Phyllis looking increasingly cursed (Jane Rose, who played Audrey, died only two years after the show went off the air), it couldn't sustain its initial success. But it also had the problem of putting Phyllis at the center of a show. Usually on an MTM sitcom, the lead character is more normal than everybody else. But Phyllis was one of the weirdest people on Mary Tyler Moore; Mary and Rhoda both stood around and gaped at her endless self-delusion. If you look at the pilot of Phyllis, it's clear that the writer/creators Ed. Weinberger and the late Stan Daniels are trying to keep the qualities that made Phyllis interesting, but that means in practice that for much of the episode, other characters are playing straight man to her, instead of the lead character playing the straight man to the other eccentrics. That was why the introduction of Mother Dexter helped the show, because she was the only character who could make Phyllis look normal by comparison. But even so, as the series went on, Phyllis's character had to be softened to make her a more plausible sitcom lead, and when the show was canceled, some insiders expressed the opinion that it had softened Phyllis to the point of losing what made her popular in the first place.
Still, Cloris Leachman is great, and you can see why MTM and the network would have wanted to give her a spinoff: she was only available for a few episodes a year on Mary Tyler Moore (she was always credited as a "special guest star" when she appeared), and by giving her a show they could have her for a full 22 episodes. Perhaps it would have worked out better to create a new character for her, but that's hindsight, and anyway the audience probably wouldn't have accepted her as a non-Phyllis character at that point. The show also gets points for retaining Lisa Gerritsen as Phyllis's daughter Bess (who had a fairly prominent role in the very earliest Mary Tyler Moore episodes, but didn't appear very often in subsequent seasons) and for casting Henry Jones, who was so great in Frank Tashlin's The Girl Can't Help It and Will Success Spoil Rock Hunter? Oh, and I've frequently offered praise for Stan Daniels' theme song.
Here's the prologue (with the guy who played the minister in "Chuckles Bites the Dust"), title sequence and Act 1:
And here's Act 2 and the closing credits: