Forms the portal vertex of the capsid and plays a role in governing correct capsid geometry (PubMed:26616586). This portal plays critical roles in capsid assembly, genome packaging, head completion protein attachment, and genome ejection (By similarity). The portal protein multimerizes as a single ring-shaped homododecamer arranged around a central channel (By similarity). Binds to the terminase subunits to form the packaging machine (By similarity). Homododecamer (By similarity). Interacts with the major capsid protein (Probable). Forms the portal complex located at one vertex of the capsid. Belongs to the phage portal family.