The spelling of the word "incendiously" can be explained using the International Phonetic Alphabet (IPA). The first syllable "in-" is pronounced with the vowel sound /ɪ/, as in "sit". The second syllable "-cen-" contains the consonant cluster /sɛn/, pronounced as "sen". Lastly, the final syllable "-di-ously" is pronounced with a long /i/ sound followed by the /ʃəs/ sounds of "shuss". Therefore, the correct phonetic transcription of "incendiously" is /inˈsɛn.di.əs.li/ with emphasis on the third syllable.