This paper brings novel data to bear on whether nominal concord relationships are formed in the narrow syntax or post-syntactically. In Guébie, a Kru language spoken in Côte d’Ivoire, nominal concord marking on non-human pronouns and adjectives is determined not by syntactic or semantic features of the concord-triggering noun, but by the phonological form of the noun. Specifically, concord marking on pronouns and adjectives surfaces as a vowel with the same backness features as the vowels of the head noun. Assuming that syntax is phonology-free (Pullum & Zwicky 1986, 1988), the fact that we see phonological features conditioning nominal concord in Guébie means that nominal concord must take place in the post-syntax. I expand on post-syntactic models of nominal concord in Distributed Morphology (Kramer 2010, Norris 2014, Baier 2015) showing that when combined with a constraint-based phonology, such an approach can account for both phonologically and syntactico-semantically determined concord systems. Additionally, the proposed analysis includes a formal account of ellipsis via constraints during the phonological component.