All of the world's spoken languages make consistent use of a relatively narrow set of contrastive speech sounds—phonemes. Here, we argue that phonemes constitute cognitive tools, supporting, guiding, and extending speaker cognitive capacities. We outline commonalities between phonemes and other cognitive tools, which include tendencies in their usage based on biological constraints, their extensive variation across cultural lineages, their criticality to the efficient transmission of information, and their importance in the scaffolding of various cognitive capacities. Studies of the commonalities of phonological systems reveal the physical and biological underpinnings upon which the tools of phonemes are necessarily predicated, and the constraints on their cross-cultural refinement. Our view complements cognitive linguistic perspectives on other cognitive tools, and on human perception and consciousness more broadly, by emphasizing the sounds of speech themselves.