Phuck You!

Why have silent letters? Isn't the whole point of a letter to represent a sound, almost like the equivalent of a musical note? Why add letters to words that aren't supposed to be there? Also why combine two letters to make the sound one letter already makes? Like ph sounding like f. Well there was already fucking f so why do the whole ph thing? Why is it phone and not fone? How do these words get decided upon anyway? Why did phone get the whole ph thing and not fuck?