The synchronic distribution and diachronic trajectory of Homeric -phi(n) have been the source of long-standing debate, with the result that scholarly opinion has yet to settle on a consensus regarding the morphosyntax of forms realized by this marker. Some maintain that forms in -phi(n) are adverbs, while others contend that they are nouns. Evidence from agreement and prepositional phrases shows that the latter analysis is correct. Homeric -phi(n) is therefore a case exponent. More specifically, it is an oblique case marker that realizes genitive or dative case in the singular, dual, or plural across all three grammatical genders. Since other case markers exist in the language for realizing genitive and dative case, forms in -phi(n) are an example of morphological overabundance, that is, the realization of a paradigm cell by more than one word form. This synchronic analysis has diachronic consequences, in as much as it now becomes clearer that -phi(n) continues the instrumental plural case marker */-bɦis/ and not the adverbial suffix */-bɦi/.