* ch: This is a single phoneme, representing the sound /tʃ/
* a: This is a single phoneme, representing the vowel sound /æ/
* t: This is a single phoneme, representing the sound /t/
* t (second one): This is a single phoneme, representing the sound /t/
* er: This is a single phoneme, representing the sound /ər/
Therefore, "chatter" has 5 phonemes.