I'm not usually one to speak bluntly, but, at least for Japanese, speaking from a lot of experience, this is flat out the wrong approach.
Older books like the romanzied "Japanese for Busy People" took this approach. I started with this book, it felt easy at the time, but it was immensely impractical - you don't build up enough of a base to learn from any other material. It's completely useless. After over a year, in a formal setting, I ultimately decided to just completely start over.
Currently Japanese courses mostly just focus on Hiragana and Katakana, since material for children usually has pronunciation guides over the kanji anyway. This is workable, but it just gives you no leverage where you could have some - you end up memorizing a thousand indiviaul words, some of which maybe kind of sound similar in parts, when you could instead learn a dozen charcters, and know that they share root words. Phoenetic approaches work for children who are in a situation where they can memorize from immersion with native speakers, and have additional clues like context and intonation to emphasize root words, to pick up new vocabulary.
When I started studying Chinese, we instead went with a "radicals-first" approach, and after just a short time of that, my Japanese vocabulary exploded - I could suddenly pick out all the seafood on a menu, and I started asking people mid-conversation "oh, does that use these characters?", and I could understand what it meant without them having to struggle to translate to English: Heart+Electric+Map - it's probably an electrocardiogram, especially if we're talking about hospitals. If you haven't learned the kanji, you don't even know if you can make that association from the sounds, much less how to ask that question.
That's how you get to fluency, by building up a foundation that lets you learn without active study. You can't get there by avoiding the basis of word composition in the language. Apologies if my frustration with characters-last approaches came through a little strong - they wasted a lot of my time.