The existence of language-specific abstract sound-structure units (such as the phoneme) is largely uncontroversial in phonology. However, whether the brain performs abstractions comparable to those assumed in phonology has been difficult to ascertain. Using intracranial electroencephalography (EEG) recorded during a passive listening task, this study investigates the representation of phonological units in the brain and the relationship between those units, auditory sensory input, and higher levels of language organization, namely morphology. Leveraging the phonological neutralization of coronal stops to tap in English, this study provides evidence of a dissociation between acoustic similarity and phonemic identity in the neural response to speech. Moreover, leveraging morphophonological alternations of the regular plural and past tense, this study further demonstrates early (<500ms) evidence of dissociation between phonological form and morphological exponence. Together these results highlight the central nature of language-specific knowledge in sublexical language processing and improve our understanding of the ways language-specific knowledge structures and organizes speech perception in the brain.