In late-insertion, realizational models of morphology such as Distributed Morphology (DM), the insertion of Vocabulary Items (VIs) is conditioned by cyclic operations in the syntax. This paper explores whether an isomorphic relationship can be established between cyclic operations such as phases and prosodic domains. In the spirit of D’Alessandro and Scheer’s (2015) proposal of a Modular Phase Impenetrability Condition (MPIC), we strive to provide an analysis in which prosodic boundaries in even smaller, word-level-like syntactic structures—the ‘lexical domain’—can be identified solely within the syntax. We propose a DM-account for the distribution of nominal plural exponency in German, which reveals a dominant trend for a trochaic-foot structure for all but -s-plural exponents (Wiese 2001, 2009). Inspired by Gouskova’s (2019) and Svenonius’ (2016) work concerning the prosody–morphology interface, we argue that the index of a Prosodic Word ω in non-s-plurals is associated with a specific feature configuration. We propose that only a n[+pl(ural)] configuration, in which the nominalizing head n hosts the SynSem-feature Num(ber)[+pl(ural)], rather than a general cyclic categorizing phase head such as n, indexes a Prosodic Word ω for nominal plural exponents in (Standard) German. Based on this empirical evidence from German plural exponency, we argue that (i) prosodic boundaries can be established directly by syntactic structures, (ii) these prosodic boundaries condition VI insertion during the initial stages of Spell-Out, and (iii) prosodic domains are based on individual languages’ syntactic structures and feature configurations, and are thus relativized and language-specific in nature.