Phonetics and memorization can complement each other. You use phonetics with the unfamiliar words and memorization with the common words. All words would ideally move from the former category to the latter category over time.
Cuh-Cuh-Caaaat may bother you, but imagine the frustration of dealing with a kid who can read one memorized book fluently while basically having no clue how to deal with an unfamiliar text. The goal of learning isn't to keep kids dependent upon teachers. You have to give them the tools to branch out.
Besides, English is so much more enjoyable once you get a taste for how the syllables flow.