Virgina Marriage Database on MyHeritage has the date of marriage as 18 Feb 1771.
Find A Grave Memorial# 69563663
Departed this life in the forenoon of Saturday the 15th of September, 1821, at 9 o'clock, in his own house, in Clarke county, Kentucky, Jacob Fishback, in the 73d year of his age. He was born in Culpepper county, Virginia, on the 14th day of April, 1749. He had been married more than fifty years to Phebe Morgan, who survives him, and was 70 years old two days before his death, by whom he had eleven children,* whose living offspring at his death amounted to 68 persons; and with the exception of two infant children, who survived but a few weeks after their birth, there had been no burial in his white family since his marriage; except one daughter-in-law. He bad been a practical believer in the Christian Religion for about fifty-five years, and a member of the Presbyterian Church about thirty-seven, and his life was a perpetual commentary on the sincerity of his faith.
* The names of his sons and daughters are: William Fishback, John Fishback, James Fishback, Annie Price, Elizabeth Mason, Jesse Fishback, Charles Fishback, Hannah Taylor, Lucy Stonestreet, and Samuel D. Fishback. -- An Outline of the History of the Church in the State of Kentucky, Bishop and Rice.
Jacob FISHBACK and Phebe MORGAN were married on 19 February 1771.78 Phebe MORGAN, daughter of William MORGAN, was born on 13 September 1751 in Fauquier County, Virginia.78,79 She died on 16 August 1837 at the age of 85.78
Said to be the daughter of William Morgan.