Plankton communities in the Philippines occupy a critical ecological position in one of the world's most biologically diverse marine regions. Situated within the Coral Triangle and traversed by the Western Pacific Warm Pool, Philippine waters support extraordinary phytoplankton and zooplankton assemblages that regulate primary production, mediate carbon fluxes, and sustain the productivity of pelagic and coastal fisheries. Yet these communities are shaped by complex interactions among the Southwest and Northeast Monsoons, seasonal upwelling, El Niño–Southern Oscillation (ENSO) events, eutrophication, and the proliferation of harmful algal blooms (HABs), particularly Pyrodinium bahamense var. compressum causing paralytic shellfish poisoning across coastal provinces. This review synthesizes published knowledge on phytoplankton diversity, zooplankton assemblage structure, HAB ecology, nutrient–plankton interactions, and the roles of plankton in biogeochemical cycles within Philippine marine and freshwater ecosystems. We further evaluate the impacts of eutrophication in enclosed bays such as Manila Bay and Laguna de Bay, coastal upwelling dynamics in the Visayas and Mindanao Seas, meroplankton contributions to larval connectivity, and emerging threats from climate change and land-based pollution. Knowledge gaps, monitoring priorities, and research directions including molecular approaches, autonomous sensing, and citizen science are identified. Integrative and long-term ecological research on Philippine plankton is urgently needed to support evidence-based marine spatial planning, fisheries management, and coastal conservation policy.