During the Battle of the Wilderness in 1864 his horse was killed from under him. While leading a charge at Laurel Hill during the Battle of Spotsylvania, Phelps was wounded and taken prisoner. However, he was later rescued by General Phillip Sheridan's cavalry under the immediate command of Brigadier General George Armstrong Custer. Phelps received the Medal of Honor for valor at the Battle of Spotsylvania Court House on May 8, 1864.