Phonetic spelling implies that one pronunciation is correct over all other alternatives, that certainly would not work for anything close to current-day english
Phonetic spelling implies that there's at least one pronunciation that correlates 1:1 to spelling, but it certainly does not rule out different pronunciations. Other pronunciations can also be 1:1, if they shift in parallel ways which actually isn't that unlikely, or they can do their own thing, the existence of a 1:1 version is still helpful even there. German-speaking Swiss share their written language with Germans (with some trivial exceptions like having cleared out the ß) but they are perfectly capable of talking in a way that is 100% indecipherable for Germans who haven't spent years learning (and even when Germans have lived their half their lives there trying to adopt the local pronunciation mapping is frowned upon).
> German-speaking Swiss share their written language with Germans ... but they are perfectly capable of talking in a way that is 100% indecipherable for Germans
You are talking there of a proper language on one side, and a bunch of non-codified dialects who never got any written form.
Yet those dialects tend to deviate from the standard language in very regular ways, even if they are perfectly incomprehensible to the uninitiated. When some new term appears in the standard language, speakers sharing the same dialect will independently shift it in the same way.
You seem to read "phonetic spelling" as using an alphabet that can encode any utterance in a reproducible way, like the International Phonetic Alphabet. I'd call that phonetic encoding, not phonetic spelling. One is explicitly language neutral, the other can be wildly language specific, but still very regular within the language specific ruleset. And those language specific rulesets usually come with a wide variety of "inofficial" variants used by regional dialects, most of which still being far more regular and internally consistent than the mess that is English.
