Final answer:
The Supreme Court's phrase "separate but equal" from the Plessy v. Ferguson case in 1896 legalized racial segregation, allowing for de jure segregation and inferior treatment of African Americans until overturned by Brown v. Board of Education in 1954.
Step-by-step explanation:
The Supreme Court used the phrase "separate but equal" when it legalized segregation in the 1896 case of Plessy v. Ferguson. This doctrine established that racial segregation did not violate the Equal Protection Clause of the Fourteenth Amendment, provided that the segregated facilities for both races were equal.
The case was a pivotal moment in the establishment of de jure segregation in the United States, allowing for discrimination and inferior treatment of African Americans under the guise of equality. The decision reinforced state laws that required segregated facilities and stood as the law of the land until it was overturned by the Brown v. Board of Education decision in 1954, which ruled that "separate educational facilities are inherently unequal."