What's it called when pronunciations are sounded out with normal letters?
I don't mean IPA symbols (which I can't read) but rather characters from a normal alphabet being used to phoneticise a word, e.g. excerpt is pronounced "[EK] + [SURPT]". What would this be called? Letter-based phoneticisation?
The IPA is a lot more efficient in that regard! It's international so it's valid for all languages, whereas phonetic spelling is easier to learn but changes from language to language.
Even within England, the difference in pronunciation from region to region means that there can be no 'true' pronunciation. Add to that the weird a/o vowel, the t/d thing and odd emphasis on 'r's at the ends of words that many Americans use, or the wholesale reassignment of vowel sounds that New Zealand uses, and you'll find that any 'proper' way to spell things is not how the majority of the world says it.
The biggest issue is that English is an exceptionally fluid spoken language, but began solidifying as a written language hundreds of years ago.
Even if we did a do-over of the spellings in written English, it would fall out of sync with the spoken language very quickly.