Voynichese is a numeric cipher?

[JoeyB]

I interpeted it as he had trouble doing it by hand since machine decode ostensibly takes seconds: FIRE IS THE PURE AND VOLATILE PRINCIPLE THAT CONSUMES MATTER TO RELEASE LIGHT AND HEAT WHILE TRANSMUTING BASE SUBSTANCE INTO ASH AND SPIRIT

This is exactly the source phrase.

So, it is decodable, but the question remains how quickly a 15 century reader using tools and technology of their time would be able to decode it. From what I've seen so far, this would be a slow process, certainly not faster than one sentence in a few minutes, in edge cases (several possible anagrams for a few words) could take much longer or multiple viable interpretations could co-exist.

Agreed, the scribe doing that for 200+ pages is going to have a major headache. And the longer the word, the harder to unscramble the anagram so the headache scales.