This vowel team says /ō/, as in “oath”. It most typically occurs at the beginning or middle of syllables and words. 

/ō/, /ō/, /ō/, oath

Vowel teams work together to make one sound, but not all vowels next to each other are a vowel team.  When OA is at the end of a word, it actually forms two sounds, each in its own syllable, as in “boa”.