Phonological neighborhood density is known to influence lexical access, speech production as well as perception processes. Lexical competition is thought to be the central concept from which the neighborhood effect emanates: highly competitive neighborhoods are characterized by large degrees of phonemic co-activation, which can delay speech recognition and facilitate speech production. The present study investigates phonetic learning in English as a foreign language in relation to phonological neighborhood density and onset density to see whether dense or sparse neighborhoods are more conducive to the incorporation of novel phonetic detail. In addition, the effect of voice-contrasted minimal pairs (bat-pat) is explored. Results indicate that sparser neighborhoods with weaker lexical competition provide the most optimal phonological environment for phonetic learning. Moreover, novel phonetic details are incorporated faster in neighborhoods without minimal pairs. Results indicate that lexical competition plays a role in the dissemination of phonetic updates in the lexicon of foreign language learners.