Missing from the body of literature on contact-induced phonological influence are studies that examine language variation as it occurs in speech production among members of a speech community. This study uses a corpus of naturally occurring Spanish/English code-switched discourse to determine whether cross-language phonological effects are evident in the data. Specifically, 2629 tokens of word-initial /d/ were analyzed in spontaneous interactions to identify the linguistic factors that condition the variable reduction (unreduced [d], reduced [ð]/Ø) of /d-/ in Spanish words. Cognate words (doctor) were found to reduce significantly less often than non-cognate words (después ‘after’). In addition, a significant effect is found for a novel, contextually informed measure that estimates words’ proportion of use in online contexts promoting reduction (Frequency in a Favorable Context). The greater a word’s prior exposure to online contexts promoting reduction, the greater the likelihood of reduced articulations. Indeed, this work argues that the distinction between cognates and non-cognates in fact emerges through this cumulative effect of significantly different patterns of use in discourse. Cognate /d/ words are used overall (considering speakers’ use of both English and Spanish) less often in contexts that promote reduction than non-cognate words. As a result of the diminished net exposure to reducing environments, per usage-based grammar, the lexical representations of cognate words have strengthened non-reduced exemplars ([d]). The distinct rates of variation for the word categories thus emerge from distinct usage patterns. This paper proposes such a focus on usage patterns within naturally occurring speech for phonological analyses within contact linguistics.