The Romans Changed the Alphabet

The early romans borrowed the etruscan alphabet around 600 b c, when rome was barely a city. And they began to modify the alphabet to make it fit latin which was a quite different language from the etruscans. Up to this point, the sixth letter of the alphabet represented the w sound we in greek and etruscan. The romans moved this sound to nearer to the back of the alphabet, and that freed up the sixth letter. So our modern letter f with the f sound was born. But for those greek words which were being borrowed into latin, they chose to use the p h combination to represent the original greek letter fi.