In women's speech, /t/ is realized as [tʃ] before front vowels.
Vowel qualities are /aɨeiou/. Vowels may be oral or nasal, creaky or modal, long or short: e.g. /kɨ̰̃ː/ "to go". /o/ is apparently never contrastively nasalized, though it may be phonetically nasalized due to assimilation with a nasal vowel in a following syllable, and morphologically nasalized for the second-person familiar (e.g. /kḭʃi/ 'to come', /kḭʃĩ/ 'you will come'). The preceding vowel nasalizes only if the intervening consonant is voiced, or in some words /ʃ/. Nonetheless, even voiceless fricatives and affricates are phonetically nasalized in such environments: [β̃,ð̃,ts̃,ʃ̃]; the nasalization is visible in the flaring of the nostrils.
The first vowel of a disyllable is creaky if the second consonant is voiceless (except for /ʃ/); only when C2 is voiced or /ʃ/ can there be a contrast between creaky and modal vowels in V1. The irregular behavior /ʃ/ is apparently due to it deriving from proto-Mixtec from both voiceless velar */x/ and voiced */j/ ("*y"). It is words in which /ʃ/ derives from *j that allow V1 to be nasalized or contrastively modally voiced.
Gerfen, Chip. 1999. Phonology and Phonetics in Coatzospan Mixtec (Studies in Natural Language and Linguistic Theory 48). Springer-Science+Business Media, B.V.
Gerfen, Chip (2001). "Nasalized Fricatives in Coatzospan Mixtec". International Journal of American Linguistics. 67 (4): 449–466. doi:10.1086/466471. JSTOR1265756. S2CID144266099.
Pike, Eunice V. & Priscilla C. Small. 1974. Downstepping terrace tone in Coatzospan Mixtec. In Ruth M. Brend (ed.), Advances in tagmemics (North-Holland Linguistic Series 9), 105-34. Amsterdam: North-Holland.