Phillips died in Minneapolis on Wednesday, Publicist Gene Willis of Universal Uclick said.
The "Dear Abby" column appeared in 1,000 newspapers as far away as Brazil and Thailand.
In her book "The Best of Abby," Phillips commented that her years writing the column "have been fulfilling, exciting and incredibly rewarding. ... My readers have told me that they've learned from me. But it's the other way around. I've learned from them. Has it been a lot of work? Not really. It's only work if you'd rather be doing something else."
Her column had competed for decades with the advice column of Ann Landers, written by her twin sister, Esther Friedman Lederer. While Ann Landers' response was homey and details, Abby's replies were often flippant one-liners.
Phillips' family revealed in 2002 that the newspaper writer had been diagnosed with Alzheimer's disease. By then, Phillips' daughter, Jeanne Phillips, who had helped her mother with the column for years, was the sole author.
The Associated Press contributed to this report.