Many Indonesians are confused: which is the correct spelling: photo, foto, or poto. In fact we can find all three variants. The official spelling is foto, but, as many Indonesians cannot pronounce the sound /f/, the word is often rendered in pronunciation, but also in spelling as poto. The spelling photo mimics English usage, but is wrong.
English has a number of redundant letters or letter combinations (graphemes), and English is also a very conservative languages in regards to its spelling system. Many English words are still spelled the way they were pronounced hundreds of years ago, and words of Greek origins often still reflect their original Greek spelling.
The fact that the word ‘character’ is written with the grapheme ch (and not with the letter K) is because in Greek it is written χαρακτήρ where the first letter is the letter Chi (χ). For the same reason is the word ‘mith’ written with the grapheme th because it is derived from Greek μῦθοι where the third letter is the letter Theta (θ) – which is not pronounced like th in English. And then are the numerous English words that contain the grapheme ph because they are based on the Greek letter Phi (φ) such as phantasy which is derived from Greek φαντασία.
The phoneme-grapheme correspondences of Chi, Theta and Phi in English are as follows: Chi is represented by the grapheme ch which corresponds to the phoneme (sound) /k/ (character, Christ, chiropractic). Theta is represented by the grapheme th, and is pronounced /th/ (myth, theology, pathology). Phi is represented by the grapheme ph which corresponds to the phoneme /f/ (phase, phonetics, orthography).
In many European languages the phoneme-grapheme correspondences of Chi, Theta and Phi differ from English. Among European languages the dental fricative /th/ is only known in English, Spanish, and Greek. Therefore the Theta will in most European languages be pronounced /t/. As many European languages also have a much more modern orthography (spelling system) as compared to English, a word such as ‘theology’ which is derived from Greek θεος and λογος (theos [God] and logos [word, teaching]) is in Danish, Norwegian, Swedish, spelled teologi, and in Hungarian, Italian, Polish, Portuguese, and Spanish teologia.
While in English the grapheme ph is always used to render the Greek letter phi (φ) as in philosophy, telephone, paragraph, photo, graphite, and phenomenon other European languages render the Phi phonetically as /f/. In Dutch, for instance, the same words are written filosofie, telefoon, paragraaf, foto, grafiet, and fenomeen—a double vowel indicates that the vowel is long.
Greek words were introduced into the Indonesian language through Dutch and not English, and hence they closely resemble their Dutch counterparts: filosofi, telepon, paragraf, foto, grafit, and fenomena.
You may have noticed that Dutch ‘telefoon’ is not spelled with an /f/ but with a /p/. This is because the Malay language from which Indonesian is derived does not know the phoneme /f/, which in many cases is rendered as /p/: pikir (think) and paham (understand) from Arabic ‘fikr’ and ‘fahm’, kopi (coffee) from Dutch ‘koffie’, etc.
So, can you conclude that when you have words of Greek origin containing ch, ph, and th, the corresponding Indonesian word is always spelled similar to the English word, but with k instead of ch, f instead of ph, and t instead of th? This is indeed often the case. But not always: blasphemy (from Greek βλάσφημος) is penodaan agama and not *blasfemi.