You can't really do a phonetic spelling without switching to a syllabary like japanese uses. Even though Japanese uses a syllabary & can be converted to roman/english letters using something called romanji
here is nice little article nearly highlighting some problems in using it that doesn't require you to know any japanese or the associated charactersets to grasp. Put in different terms, english has 26 letters &
44 sounds, by contrast japanese has two sets of 46 characters plus around 2000 or so kanji and
84 sounds. How many people do you think are going to learn a whole new syllabary when most people don't really even know what it means when a letter has a hat line dot or whatever over it?