Phelps' son, Tim Phelps, confirmed his father's passing at Midland Hospice in Topeka, Kan.
On Saturday, another of Phelps' sons said his father had been excommunicated from the church and was on his deathbed. Nathan Phelps, who himself left the church some 30 years ago, expressed mixed emotions at the revelation.
"I'm not sure how I feel about this," he wrote in a post on Facebook. "Terribly ironic that his devotion to his god ends this way. Destroyed by the monster he made."
"I feel sad for all the hurt he's caused so many. I feel sad for those who will lose the grandfather and father they loved. And I'm bitterly angry that my family is blocking the family members who left from seeing him, and saying their good-byes."
The Westboro Baptist Church, made up mostly of members of Phelps' extended family, has become synonymous with virulent anti-gay sentiment that saw them protesting soldiers' funerals. A 2011 Supreme Court ruling said the First Amendment protected the church's right to protest at those funerals without being sued for monetary damages.
The civil rights nonprofit Southern Poverty Law Center has called the Westboro Baptist Church a hate group.