Korie Robertson -- Phil's son Willie's wife of more than 30 years -- posted the news to Facebook Sunday ... saying Phil was a man of God, who always tried to remind people that death only meant returning to God's kingdom.
She thanked fans for their thoughtful prayers ... and, she promises the family will continue to honor him and his legacy.
His family revealed he was diagnosed with Alzheimer's disease back in December in an episode of the "Unashamed with The Robertson Family" podcast.
Jase Robertson previously said Phil was also suffering from a blood disease that was causing health issues -- and the disease was only getting worse.
Phil's son said he famous father wasn't doing well overall and was struggling to live ... barely able to walk without crying out in pain.
Phil starred on "Duck Dynasty" from 2012 to 2017, and he founded the Duck Commander company.
A&E is rebooting the popular docuseries but in announcing the return of 'Duck Dynasty' the network made no mention of Phil.
Unclear if Phil's health issues prevented him from being involved in the reboot ... but it's worth noting he was briefly suspended from the show following a controversial 2014 GQ magazine interview where he made homophobic and racist remarks.