"She was running around, she was all dressed up, we swapped necklaces," Rivers told ABCNews.com. "I adored her. It's nice thinking that three weeks ago we were sitting and laughing. It was like talking to a girlfriend."
"She had such a good, full happy life," Rivers said. "She had a great time to the very end."
Diller died Monday at the age of 95, her manager confirmed to ABC News. She died at her home in Brentwood, Calif., where she had been in hospice care, after a fall.
She won't be soon forgotten. The anointed Queen of Comedy paved the way for other female stand-ups, including Rivers.
"She was the mother of all modern day female stand-up comics," Yael Kohen, author of "We Killed: Rise of Women in American Comedy," told ABCNews.com. "There were funny women before her, but most of them combined song and dance with their act. To be a woman who just talked on stage, that was very groundbreaking."
Diller was not afraid to share the stage with other funny women.
"I do think when I was coming up she was so strong and so generous to allow me to come up," Rivers said. "There were certain other comedians who were not so thrilled to see me come along. But she was such a champion, such a pleasure and joy."
Diller was also a consummate professional.
"She was such an inspiration," Rivers said. "She was always on top of everything. She never sat on her laurels. She never let her material get stale. She had a great work ethic. The act constantly changed and evolved. She was always so prepared. She never disappointed you."
Diller began her career in 1952, at the age of 37. At the time, she was married with five children, and her husband, Sherwood Diller, was chronically unemployed.
"Poverty, and my husband, my husband, Sherwood Diller, insisted that I become a comic," she told NPR's Lynn Neary in 2006 about her reasons for becoming a comedian. "The thing is, I had been doing [comedy] all my life without realizing it because I'm a born comic. I was born funny. I think funny, and ... my attitude toward life was funny."
Diller rose to fame with her TV specials alongside her mentor Bob Hope, in the 1960s. Later, she starred in her own show, "The Phyllis Diller Show," as well as the variety show "The Beautiful Phyllis Diller Show." She was also a regular on "Laugh In."
Known for her loud cackle and long cigarette holder, Diller created the stage persona of a wild-haired, crazily dressed housewife who cracked jokes about her age and appearance, bad cooking and husband "Fang."
Off the stage, Diller was slender and not unattractive, Kohen said. She played down her looks and made self-deprecating jokes in order to be accepted by audiences. And they did accept her.
"She supported half the world and her five kids," Rivers said. "And she did it on the road. It was very hard for a woman on the road, and she really knew the loneliness of the road. She was an emancipated woman. And she managed to have a private life."
In her private life, she was a gourmet cook, an accomplished pianist and a painter.
She would stay up in the middle of the night, drinking martinis and painting," said Kohen, who got one of the last interviews with Diller in late 2009, when she visited with the comedian in her Brentwood home, where she had a large painting of Bob Hope on her wall.
"She didn't hold back," Kohen said. "When she would laugh, I was so afraid she was going to pass out because her laugh was so deep and it overtook her whole body."