Growing up, the Friedman Twins - as the popular girls were known - were inseparable. They dressed alike, shared purses and dates, and often slept in the same bed. Eppie broke her arm when she was 11, her daughter Margo Howard told the Miami Herald, but Phillips later thought that the injury had happened to her.
"The would tell each other's stories, and in their minds their lives became interchangeable," wrote Howard, who for a time penned the Dear Prudence advice column on Slate.com, which is owned by The Washington Post Co.
When the sisters graduated from high school in 1936, the yearbook said it all. Next to Popo's picture was the message "Always with Eppie." Next to Eppie's was "Always with Po-Po."
The girls went off to school - together, of course - to Morningside College, where they co-authored a gossip column, the Campus Rat, in the student newspaper. Just before their 21st birthdays, they left college to be married in a double ceremony followed by a double honeymoon.
Their wedding - which, according to Howard, was attended by 750 guests plus onlookers and mounted police - was preceded by a bit of drama. Popo had been with Morton Phillips, heir to his family's liquor business, for several years, but Eppie subbed in a new groom at the last minute. After accepting a date with a buyer at the clothing store where the girls shopped for their wedding veils, she ditched her fiance and married Jules Lederer, who would later form Budget Rent a Car.
Phillips told the Los Angeles Times that she had never expected to have a career, but that after getting married she thought "there has to be something more to life than mah-jongg." In addition to raising her two children, she volunteered with the Red Cross's Gray Ladies.
By the mid-1950s, Phillips' sister was living in Chicago and had taken to reading a column in the Chicago Sun-Times called Ask Ann Landers. When she learned that the columnist had died, she entered a competition to become the new Ann Landers - and won. Lederer's first installment of the column appeared in the newspaper on Oct. 16, 1955.
Lederer enlisted her sister's help to keep up with the onslaught, but the paper soon asked her to stop the outsourcing. And so it was that in the winter of 1956, Phillips went after a column of her own. As Time magazine told it:
"From a chauffeured yellow Cadillac convertible in front of the San Francisco Chronicle building last winter stepped a shapely brunette wearing a little black dress by Dior and the scrutable smile of a woman who knows what she wants."
What she wanted was to take over for Molly Mayfield, the advice-giver the paper published at the time. When an editor gave her a stack of old columns for a tryout, Phillips ran to her husband's office and in two hours wrote her own responses to 70 letters. The editors enjoyed her work so much that they gave the column over to her practically on the spot.
For her alter ego's name, Phillips drew upon the Bible ("And blessed be thy advice," it was said of Abigail) and American history (the eighth's president's last name just sounded elegant). Abigail Van Buren would nip at Ann Landers' high heels until Lederer's column ended with her death in 2002.
What the sisters didn't want was to be compared, but to many the urge was irresistible. Time magazine described Phillips' column as "slicker, quicker and flipper" than her sister's. Their competition provoked a rivalry and long spells when the sisters did not speak to each other.
"For seven years," Abby wrote, "my career flourished but I walked around with a hole in my heart."
Yet their bond was undeniable, and there were other periods when the sisters faxed each other almost every day.
Phillips' survivors include her husband of 73 years, the person to whom she said she turned for advice; her daughter, Jeanne Phillips, of Los Angeles, who now writes the Dear Abby column; four grandchildren; and two great-grandchildren. Her son Edward Phillips died in 2011.
The rewards of the advice business, Phillips told the Los Angeles Times, were great.
"Every day I get letters from people who say, 'You changed my life. . . .' Now that's important."