I don't understand the sentence. Like the Ph.D as a level of education in history?
Yes. "διδακτορικό δίπλωμα" or, informally, just "διδακτορικό" means "doctorate degree". Since PhD is the type of doctorate degree awarded in History, you get this translation.
It's quite uncommon like that, whereas it's more often found in phrases like "the history Ph.D. student", "the history Ph.D. program" and so on ;)