Building Information Modeling (BIM) represents a building as a static snapshot of the model’s state. The IFC standard does not define a formal mechanism that would link the same physical element across successive phases of a building’s life cycle. Design, construction, and operation are recorded in separate IFC files, and the same element is assigned different GUIDs in each. The result is fragmentation of the element’s identity, loss of the history of property changes, and the inability to formulate cross-phase queries. This paper proposes the BIM-Phase ontology, based on the fundamental DOLCE ontology, which solves this problem by introducing a distinction between a building element as an endurant and its life cycle phases as perdurants. The ontology comprises nine classes, six object relations, and six axioms expressed in OWL 2 DL. Phase properties and relations are represented using a reification pattern, which maintains full compatibility with the expressiveness of OWL 2 DL. The ontology was validated using the example of a single-family residential building developed in Autodesk Revit. Three structural elements (external wall, floor slab, column) were tracked across three phases of the life cycle. Eight competency questions covering scalar, constitutional, and mereological changes were defined and mapped to ontology constructs, confirming that BIM-Phase enables the recording of changes and the formulation of cross-phase queries that are impossible in classic IFC.