⟨pf⟩ in German represents a labial affricate /pf/. It can be initial (Pferd, 'horse'), medial (Apfel, 'apple'), or final (Knopf, 'button').
⟨ph⟩, in the English Language and many other languages, represents /f/. Ph in English generally occurs in words derived from Greek, due to Latin transcription of Greek phi (Φ φ) as ⟨ph⟩. In Ancient Greek, this letter originally represented /pʰ/ (an aspirated voiceless bilabial plosive). In some non-standard spellings of English, like leet, ph may be used as a replacement of all occurrences of f. Exceptionally, ⟨ph⟩ represents /v/ in the name Stephen and some speakers' pronunciation of the word nephew.
The French and German languages and the auxiliary languages Interlingua and Occidental also use the digraph for Greek loanwords. In German, ph can be replaced by f; the replacement is allowed in certain cases according to the German spelling reform of 1996. In most Romance (such as Spanish) and Germanic languages, f is used in place of ph. Languages written in a Cyrillic script, such as Russian, Ukrainian, and Bulgarian, regularly use Ф ф – similar to the Greek Φ φ – where the Romance and Germanic languages use ph or f. In Welsh, ph represents /f/ in native words, but only word-initially as the result of an initial consonant mutation of a word beginning with p. Irish uses f for words of Greek origin, while ph represents the lenited form of p, resulting in the sound /f/ as well. In Vietnamese, ph is exclusively used because the letter f does not exist. In Old High German, ph stands for the affricate /pf/. In the romanizations of Indo-Aryan languages and of Thai, ph represents the aspirated sound . In the Ossete Latin alphabet, it was used for .
⟨pl⟩ is used in the Romanized Popular Alphabet used to write Hmong, where it represents the sound .
⟨pm⟩ is used for /ᵖm/ in Arrernte.
⟨pn⟩ is used in English for an initial sound /n/ in words of Greek origin such as pneumatic. When not initial, it represents the sequence /pn/, as in apnea.
⟨pp⟩ is used in romanized Korean for the fortis sound /p͈/.
⟨ps⟩ is used in English for an initial sound /s/ in words of Greek origin such as psyche. When not initial, it represents the sequence /ps/, as in ellipse. It is also used in the Shona language to write a whistled sibilant cluster /ps͎/.
⟨pt⟩ is used in several languages for /t/ in words of Greek origin, where it was /pt/. An example in English is pterosaur /ˈtɛrəsɔr/, and an exception is ptarmigan /ˈtɑrmɨɡən/, which is Gaelic, not Greek. When not initial, pt represents the sequence /pt/, as in apt.
⟨pw⟩ is used for /pʷ/ in Arrernte.
Read more about this topic: List Of Digraphs In Latin Alphabets