The Manila variety of Philippine Hybrid Hokkien (PHH-M) or Lánnang-uè is a contact language used by the metropolitan Manila Chinese Filipinos; it is primarily comprised of Hokkien, Tagalog/Filipino, and English elements. Approaching PHH-M as a mixed language, we investigate linguistically and socially conditioned variation in the monophthongs of PHH-M, focusing on the extent to which the vowel systems of the three source languages have converged. This analysis draws on data gathered from 34 native speakers; Pillai scores are calculated to assess the degree of merger. Contrary to certain predictions of prior work on mixed languages, PHH-M is found to have a unified, eight-vowel inventory distinct from any of its sources. Older women use more stable vowels across source languages, suggesting that they have led in the development of PHH-M as a mixed code; however, signs of change among younger women suggest either the endangerment of the code or its evolution in response to the community’s shifting identity. We contextualize our conclusions in relation to the sociohistory and language ecology of metropolitan Manila’s Chinese Filipino community.