and also by extension, Greek (directly in many cases -- almost every english word that starts with 'ph' was a greek word -- but also a large portion of medical and mathematical terminology)
Fun fact: russian language had no 'f' sound prior to cyrillic alphabet which has a letter for it.
Heuristically, the "rule" passes the eyeball test: philosophy, physical, photo, phrase, philanthropy, phobia, phage, phalange, phalanx, phallic, phase, pharmacy, phantom, phenomenon, phone, photons, photosynthesis, physician, physique, phytoplankton, so on and so forth
The overwhelming majority of these words are greek transliterations https://www.thefreedictionary.com/words-that-start-with-ph
(in fact I am having a hard time finding even one word that isn't -- i think "phreak" is the only one I can find)