Collaboration is an essential part of problem-based learning (PBL), but detailed understanding about how interaction between PBL participants leads to co-construction of knowledge is still quite scarce. This study attempted to address this issue by analyzing the phases of interaction between three teachers in a professional education setting solving a real-world problem over the course of seven weeks. Other data such as documents and artifacts created by the participants were also analyzed in relation to the interaction, allowing for triangulation of data as well as richer description of the advances of the interaction. What emerged were six phases that conceptually depict the interactional interplay between the actors in the process of social construction of knowledge in this PBL setting. These phases provide a lens in which to view and understand the phases of interactional interplay between PBL actors. This outcome can eventually contribute to more detailed guidance on how certain types of discourse moves can advance these phases of interaction.