PhDs are hard shem.
Remember the fact that more and more black people are getting them it doesn't mean that they are easy. All it means is that black people now have access and opportunity to showcase how smart they are and have always been.
So don't undermine, question or discredit. Just appreciate, engage and learn.
And yes we don't know everything. So don't expect that from PhD holders. Just appreciate that they know aspects of their field deeply and have contributed to a small part of innovation. You could teach them a thing or two. And they should be humble enough and be willing to learn.
Afterall a true measure of one's intelligence is the willingness to learn from others despite caste or creed.