Phillips was especially influenced by Frederick Jackson Turner who invited Phillips to the University of Wisconsin where Phillips taught from 1902 to 1908. He taught for three years at Tulane University. In 1911, Phillips moved to the University of Michigan where he taught until 1929 when he left to teach at Yale as Professor of American History until his death in 1934. In the 1920s he spent a year in Africa traveling and doing research. He received an honorary D. Litt. from Columbia University in 1929.