the meaning of "hollow phrase"

[kjc0123]

What is the meaning of "hollow phrase" in the following sentence?

The Supreme Court of the United States held in the Civil Rights Cases109 US 3 (1883) that the Fourteenth Amendment did not give the federal government the power to outlaw private discrimination, then held in Plessy v. Ferguson163 US 537 (1896) that Jim Crow laws were constitutional as long as they allowed for separate but equal facilities. In the years that followed, the Court made this "separate but equal" requirement a hollow phrase by approving discrimination even in the face of evidence of profound inequalities in practice.

[Quizmonster]

'Hollow' in this situation means 'empty'...of meaning, that is. Basically, the law stated that African Americans had to have the same facilities/advantages - but separate from those of whites. However, it was clear, in reality, that this did not exist, as the court simply ignored the glaringly-obvious fact that no such equal facilities were available.