Her lack of college or law school degrees proved to be no obstacle to her admission to the bar. According to state statute, any citizen, after reading the law in the office of an attorney, could apply. Even so, the New Jersey Supreme Court refused Philbrook’s petition in 1894 on the grounds that no other woman in the state had ever sought admission to the bar. Philbrook sought the support of the New Jersey Woman Suffrage Association and lobbied in the New Jersey legislature for a law that would allow women to practice the law. She was admitted to the bar in 1895.
Philbrook began her practice at the firm of Bacot and Record in Jersey City. She eventually opened her own office. Throughout her career, Philbrook delivered educational lectures to club women around the state about women’s legal rights. She also successfully campaigned with Mabel Smith Douglass of the Jersey City Woman’s Club for the establishment of the New Jersey College for Women in New Brunswick, which was later renamed Douglass College and is now part of Rutgers University. Philbrook relocated her practice in 1902 to Newark, and while there organized the first statewide Legal Aid Association. She was also active in the State Charities Aid Association, a coalition of public and private charitable institutions.
In 1906, Philbrook made history as the first woman appointed to practice before the U.S. Supreme Court. Her appointment was based on the constitutional claim of New Jersey women to vote. Philbrook remained professionally active for another twenty years or so, and in the 1940s renewed her campaign for an equal rights amendment to the state constitution. At the 1947 Constitutional Convention, a 75-year-old Philbrook organized a coalition of women’s groups to lobby for an equal rights provision in the new constitution. The change, from the word “he” to “person”, was cited in 1979 by the NJ Supreme Court as grounds to rule that sex discrimination was constitutionally prohibited in the state.