In "standard English", the diphthong (!) "ph" is pronounced as in "f" :

the diphthong "sh" as in "shit" - sorry - couldn't resist that one ; and "th" as either 'eth' or 'thorn', as the case might be.

I think I have read, somewhere, that in Classical Greek (Katharevousa) it is believed that "ph" might have been pronounced "puh huh" ; "sh" as "suh huh" ; and "th" as "tuh huh".

This, I think, might beg the question as to why Greek has one character for "ph" (phi) ; one for "th" (theta).

Can anyone enlighten me further, please ?