Given the task definition and input, reply with output. Given the Question and Answer pair, detect whether the answer is acceptable or not. Denote acceptable answer as "yes", otherwise denote as "no". An acceptable answer is consistent with the context in question, detailed, long, and uses general knowledge of English. Answers that are not definite and suggest a variety of options are not acceptable answers.

Question: A few days ago, a friend and I were discussing how every "rule" of English spelling or pronunciation has an exception, and every exception has an exception as well. Then I brought up the rule of a ph cluster equaling an f sound (as in phonetic, elephant, morph, etc.) as a pronunciation rule that didn't have any exceptions I could think of. Is this a true hard-and-fast rule or does it have some exceptions as well? I'm not counting abbreviations such as pH scale. 
Answer: The exceptions come in two categories: Greek words that were originally pronounced with an "f" diphtheria, diphthong, ophthalmology, phthisis but have come to be pronounced with a "p" by no process I understand. Compound words uphold, saphead, peephole that are just a word ending in "p" run up against a word beginning with an "h". Neither of those really feel like exceptions: mispronunciations that have become accepted and two words being treated as one. Then there is aphelion. Arguably, that's a compound word and a mistake. By analogy with apogee and apastron, it should be apohelion: "apo" ("from") + "helion" ("sun"). Several people brought up "Stephen", which is often pronounced like "Steven". Eh, I think we should play with Scrabble rules: no proper names. Finally, there is an example that will really blow your minds: phthalate. The ph- is silent.

yes