This is basically impossible for English, since for many vowels, the various dialects map the diaphonemes of English into mutually incompatible sets of phonemes: https://en.wikipedia.org/wiki/International_Phonetic_Alphabe... (and even that chart is underestimating the differences - tour and moor definitely have different phonemes in en-AU, even though they are allegedly from the same diaphoneme.

If you had a conservative spelling system, where each diaphoneme was mapped to a single letter, speakers of dialects with many merges (e.g. American English) would struggle to spell correctly, since they would be unable to distinguish several letters apart. If you had a simplified system, then most speakers would get confused by merges that existed in the spelling system but not in their own dialects; and speakers of more conservative dialects wouldn't be able to write sounds that are to them different.