Alexander Phoenix was born in Morristown, N.J., on February 28, 1778, the son of Daniel Phoenix, a wealthy New York City merchant, and Elizabeth Platt, who died when Alexander was seven years old. He studied law at Columbia University, graduating in 1794, but only practiced law for four years before joining his father's mercantile firm, Phoenix, Ingraham, & Nixon. In 1807, he married Martha ("Patty") Ingraham, daughter of his partner, Nathaniel G. Ingraham. They had two children, Alexander and Elizabeth (c. 1810-1874), before Patty's death in 1810.
When the firm declared bankruptcy in 1811, after several of its ships were captured by the French, Phoenix, Nathaniel Ingraham, and William Nixon, Jr., were sent to debtor's prison for two years. After his release, Phoenix began to study theology. He married Elizabeth Tappan of Massachusetts in 1817, but she died soon after the birth of their only child, Rebecca. Phoenix remarried, this time to Sarah Strong, daughter of Massachusetts Governor Caleb Strong, in 1822; they had three children. In 1824, Phoenix was ordained a Congregational minister and installed in the church at Chicopee, Massachusetts. As pastor, he led a revival of the church, bringing many new members into the church. He remained there 11 years, then moved to a pastorate in New Haven, Connecticut, and eventually retired in Harlem, New York. He died on August 31, 1863.
Phoenix's daughter Elizabeth attended Catharine Beecher's school, the Hartford Female Seminary, in the 1820s, where she befriended Harriet Beecher, with whom she would correspond for the next decade. In 1838, she married lawyer Edgar Ketchum, and they had at least five children.