The spelling of the word "Buu" follows the basic rules of phonetic transcription. The first sound, "b," is voiced bilabial plosive, IPA symbol /b/. The second sound, "u," is pronounced as a short vowel, IPA symbol /ʊ/. Finally, the last sound, "u," is also pronounced as a short vowel, but with a higher tongue position, IPA symbol /u/. Therefore, "Buu" can be spelled as /buʊ/. It is important to follow correct phonetic transcription to avoid confusion and promote accurate communication.