Phelps supported the Union during the American Civil War, but was a critic of what he regarded as the excesses of the Abraham Lincoln administration.

[2] He worked as a school teacher and principal in Virginia, then began studying law in the Middlebury office of Horatio Seymour.

[2][a] Phelps completed his legal studies with a year at Yale Law School, attained admission to the bar in 1843, and began a practice in Middlebury.

[2] Phelps practiced in Burlington with different partners at various times, the most prominent being Lucius E. Chittenden and David Allen Smalley.

[4][5] The Phelps and Smalley firm counted George F. Edmunds among the prospective attorneys who studied law under their tutelage.

[4] In 1851, Phelps was the successful Whig nominee for state's attorney of Chittenden County, defeating Democrat Leverett B. Englesby in the general election.

[2] 1880 was no exception, and Phelps was excoriated as an unrepentant Copperhead: Had he maintained his resolution to accept no political nomination, the memory of his attitude during the memory of his attitude from 1860 to 1865 might have quite died; but the Democratic nomination and his speech of acceptance, in which, with surprising want of tact, he aired afresh his old hatred of the African and attacked the Southern Republicans, white and black, with a virulence which few Southern Democrats could equal … have brought it into strong prominence.

Still stronger light has been thrown on it by the publication of a careful stenographic report of a speech made by Mr. Phelps in September, 1864, before a little club of Copperheads in Burlington.

[9] He was praised for his work as minister, which focused on restoring the congenial relationship the two countries had enjoyed prior to the American Civil War, when relations deteriorated because England was on the verge of formally recognizing the Confederate States of America.

[13] Also in 1893, he served as senior counsel for the United States before the international tribunal in Paris which considered the Bering Sea Controversy.

[15] Phelps was a highly sought after speechmaker and delivered numerous public addresses, among them The United States Supreme Court and the Sovereignty of the People at the centennial celebration of the Federal Judiciary in 1890, and an oration at the dedication of the Bennington Battle Monument, unveiled in 1891 at the centennial of Vermont's admission to the Union.

[1][16][17] At the urging of Senator George F. Edmunds, President Grover Cleveland intended to appoint Phelps as U.S. Chief Justice in 1888.

[18] In addition, New England was already represented on the Supreme Court by Horace Gray; in an era when the government was expected to reflect geographic balance, Cleveland decided to appoint someone from the western states.

[19] A funeral was held at Battell Chapel on the Yale campus; Theodore T. Munger officiated, and university president Timothy Dwight V delivered the eulogy.