A Doctor of Philosophy, (HOMEVID: The Zero Imperative) or PhD for short, was a type of qualification. (TV: Reset)
Peter Russell was a Doctor of Philosophy. (HOMEVID: The Zero Imperative)
Professor Aaron Copley gained a PhD from Harvard University. (TV: Reset)
Petronella Osgood had a PhD (AUDIO: The Sacrifice of Jo Grant) after studying at King Henry's University. (AUDIO: Power Cell)
In 2323, Georgette Gold was working on a PhD in Dalek Studies and, seeking the Doctor's help, sent a distress call to the Doctor's TARDIS, inadvertently embroiling the Fourteenth Doctor in the 2323 Dalek invasion of Earth. (COMIC: Liberation of the Daleks [+]Alan Barnes, DWM Comics (Panini Comics, 2022-2023).)