What continuing aspect of racism in the united states is illuminated by the susie phipps case?

The correct answer is hypodescent.
When it comes to the Susie Phipps case, she was denied her rights because she had one black ancestor. Hypodescent means that a person is assigned to a particular group (in this case, the 'subordinate' race) based on their skin color - hypo means 'below,' so these people are classified as being inferior to the hyper group. Susie identified herself as a white person (and she was overwhelmingly white), however, due to the fact that her great grandmother was black, she was still denied equal rights as white people.