The ‘f’ sound can be spelled in a variety of ways: f, ph, gh, ff, v, pf. Some of these are more mundane than others but this list is definitely not a complete list. This isn’t just limited to this one consonant sound. The ‘k’ sound can be spelled with a k, c, ch, ck, cc, cch, kh, and so on and so forth. But why are there so many different ways to spell the same sound?
The answer lies within the alphabet.
The modern English alphabet (the one we use with 26 letters) is a derivative of a Latin alphabet. This was originally used in Rome, however, this alphabet was based on a very visually similar alphabet utilized by the Etruscans- a civilization that was located in Italy. Prior to the Etruscans, this alphabet was actually derived from a version of the Greek alphabet used by the inhabitants of a few Greek colonies in southern Italy. In turn, the Greek alphabet was descended from the Phoenician alphabet- an alphabet that only had consonants.
While Phoenician was based on hieroglyphics- the writing system used by the Egyptians- it had a very key difference. The letters represented sounds and not words. The other major types of writing were primarily symbolic and were far more complicated to learn. An example of a modern-day language that uses a symbolic script is Chinese, as each symbol represents a word or idea.
This marked a pivotal change in the societies that ended up incorporating variations of the Phoenician script. It became easier for the ‘common-folk’ to learn or figure out how to write with the script. The simplicity of only having 22 symbols and sounds to memorize was far easier and cheaper than either having to pay a professional to read and write for you or learning it yourself. Slowly, literacy began to improve, aided by a script that made reading and writing far easier than it had been before.
But, we still haven’t answered the question of why there are so many different ways to spell the same sound. This answer is found a few thousand years after the Phoenicians.
All of the languages that I mentioned continued to develop through the ages and a few have stagnated or died out. Latin, however, is a very important one. At the peak of the Roman Empire, it reached all the way up to Britain, or Albion as it was known then. The Latin alphabet was used throughout Europe and to the place where it never really stuck, the Phoenician and Greek alphabets held influence. In the modern-day, almost all of the nations and languages that are spoken in Europe use a variation of the Latin Alphabet.
English, though it is a Germanic language, has had great amounts of influence by both Latin and French (both of which are Romance languages.) Romance languages, despite the name, are actually languages that are descended from Latin. Among them are Spanish, French, Italian, Portuguese, Romanian, etc. This is exemplified in the sheer number of Latin words in English (there are 4 in this sentence itself.)
As one of the most spoken languages in the world, as well as the main language of one of the nations that once was a very prolific colonizer, English has had great reach to almost all corners of the world. While the languages that are spoken in Europe share an alphabet, languages in the Americas, in India, in Japan, in Vietnam, in Thailand, etc. do not have similar alphabets at all. This creates a dichotomy where words from languages with similar alphabets are faithfully translated into English whereas more ‘exotic’ words are often simplified into their phonetic spelling in the majority of cases.
This mishmash of languages that English has cobbled together through its many years of existence is unique in the fact that it already had the infrastructure to incorporate a very different language into itself, nearly seamlessly from when Britain was invaded by the Normans. Spellings were preserved then and they remain preserved for the most part, even now.
The motley of letter combinations that make up English are a unique effort that the language has made to preserve the original spellings of words. Without the ability of these alphabets to so quickly adapt to variety of sounds, it is very likely that English never would’ve been able to accumulate such a variety of words.