No, Brigham Young, the second president of The Church of Jesus Christ of Latter-day Saints (LDS Church), was not stabbed by a son named Phineas. While Brigham Young did have many children (he had 55 children with several wives), there is no historical record or evidence suggesting that one of his sons named Phineas, or any other son, stabbed him.
Brigham Young’s life was filled with challenges, including some strained relationships with his children, but there are no accounts of such a violent incident occurring with one of his sons. Phineas Young, one of Brigham Young’s sons, was known to have had disagreements with his father, particularly about matters of church leadership, but there is no indication that any such violent act ever took place.