Phelps was born in Litchfield, Connecticut. He studied at Yale University and served as a military paymaster during the War of 1812. He then settled in Middlebury, Vermont and became a lawyer, soon entering politics. He served in the Vermont State House from 1821 to 1832, as a judge on the Vermont Supreme Court from 1832 to 1838, and as a member of the Vermont Senate from 1838 to 1839. In 1839 he gained a seat in the U.S. Senate from Vermont and served there until 1851. During that time he chaired several committees. He returned to the United States Senate in 1853, having been appointed to fill the unexpired term of Senator William Upham, who had died. However, this was disputed by some, and in 1854 he was forced to resign when a senate committee ruled that he was not entitled to the seat. He died the following year in Middlebury. His son, Edward John Phelps, was a lawyer, politician and diplomat.