The English language doesn't use phonetic spelling at least partially because there would be so many different possible ways to spell words that it would make it hard for people to understand each other. There are so many different possible ways to spell English words largely because English uses a lot of words from very different sources — from Germanic to Latin to Greek. For instance, based purely on the way it sounds, the word "scissors" could theoretically be spelled about 80 million different ways, including "sizerz" "schiesourrhce" and "cisers." This is only theoretical though, because to reach all 80 million possibilities a person would have to use letters in incorrect ways, like using the "z" at the end of a word to make an "s" sound.
More about pronunciation and English:
- Between about 1350 and 1500 CE, there was a radical shift in the way that English vowels were pronounced called the Great Vowel Shift. For instance, the sound "ee" went from sounding like the "a" in "plate" to the way it's now pronounced in "feet." It's not entirely clear why this happened, but it led to many of the strange conventions in modern English spelling — for instance, why "plough" and "through" can have the same "ough" spelling but are pronounced very differently.
- There are about 20 different ways of spellings of Shakespeare's name found in texts from his lifetime, with 6 variations (including abbreviations) of his signature.
- English also has a lot of strange spellings and pronunciations because it has so many loanwords, many of which are spelled phonetically. For instance, the word "jacket" comes from the French "jaquette," but is spelled like it sounds in English.