為什麼phantom與fantastic是同一詞源，但第一個輔音的寫法不同？

12-28

如題，今天突然發覺這兩個詞很像，在etymoline上搜索發現它們的確是同一個詞源的，然而為什麼phantom里第一個輔音轉寫成了ph，但fantastic中卻是f？

謝邀。
fantastic (adj.)
late 14c., "existing only in imagination," from Middle French fantastique (14c.), from Medieval Latin fantasticus, from Late Latin phantasticus "imaginary," from Greek phantastikos "able to imagine," from phantazein "make visible" (middle voice phantazesthai "picture to oneself"); see phantasm. Trivial sense of "wonderful, marvelous" recorded by 1938. Old French had a different adjective form, fantasieus "weird; insane; make-believe." Medieval Latin also used fantasticus as a noun, "a lunatic," and Shakespeare and his contemporaries had it in Italian form fantastico "one who acts ridiculously."
phantom (n.)
c. 1300, fantum "illusion, unreality," from Old French fantosme (12c.), from Vulgar Latin *fantauma, from Latin phantasma "an apparition" (see phantasm). The ph- was restored in English late 16c. (see ph). Meaning "specter, spirit, ghost" is attested from late 14c.; that of "something having the form, but not the substance, of a real thing" is from 1707. As an adjective from early 15c.
ph
now in English usually representing "f," originally it was the combination used by Romans to represent Greek letter phi (cognate with Sanskrit -bh-, Germanic -b-), which at first was an aspirated "p," later the same sound as German -pf-. But by 2c. B.C.E. had become a simple sound made by blowing through the lips (bilabial spirant).

Roman "f," like modern English "f," was dentilabial; by c. 400, however, the sounds had become identical and in some Romanic languages (Italian, Spanish), -ph- regularly was replaced by -f-. This tendency took hold in Old French and Middle English, but with the revival of classical learning the words subsequently were altered back to -ph- (except fancy and fantastic), and due to zealousness in this some non-Greek words in -f- began to appear confusedly in -ph-, though these forms generally have not survived.

因為發音一樣

希臘字母里有一個字母拉丁字母里沒有，這個字母發音類似於/f/，拉丁人接觸到之後，為了借用這些含有這個字母的希臘語單詞，用ph來轉寫這個希臘字母。
你可以想像一下，英語里人家是Barack Obama，而你寫成這樣在人民日報上，很多人都不知道是啥玩意，你必須寫成巴拉克奧巴馬，同樣道理。

孩子

ph的發音=f的發音啊

這是英語的common sense啊

就跟psychiatrist、psycho、psychology這裡的p不發音

以及knight裡面的K不發音一樣啊

有沒有英語辭彙造字方面的著作？這個詞是怎麼來的，比如w象徵河流，所以很多w開頭的單詞和水有關……英語辭彙浩如煙海，我非常非常希望找到一些這方面的書籍，有沒有推薦？