There is a phonetically consistent language that is highly consistent in other respects as well - #Esperanto.

People can learn Esperanto several times faster than organic languages. Studies show that a student who spends one unit of time to learn Esperanto has that investment more than repaid when going on to learn other foreign languages, because its consistency allows the concepts and mechanics of language in general to shine through the particulars.

It's often possible to guess the Esperanto equivalent of a word based on its nature. Example: if you know that `foto` is the word for photograph, you can guess that a device for making photographs is called `fotilo` - because that's how you construct the word for the maker or do-er of something.

That English has become the de facto language makes it easy for native English speakers, but so much harder for the rest of the world since English is not nearly as comprehensible.