A new, compact, and dual-band dual-polarized duplex (D³) phased array architecture is proposed in this study. In contrast to studies reported previously, this design integrates four independent beamforming systems within a single printed circuit board (PCB), enabling the proposed 1 × 4 phased array to transmit or receive simultaneously vertically and horizontally polarized signals at 28 and 38 GHz, thereby supporting concurrent, dual-band, and dual-polarized four-beam operations. In addition, the exceptional frequency selectivity of the phased array facilitates frequency-division duplex operations. By adopting a brick-type architecture, the proposed phased array achieves two-dimensional scalability, which allows it to serve either as a standalone, small-scale phased array, or as a sub-block for larger-scale arrays. A novel dual-polarized end-fire magnetoelectric dipole antenna was developed as the radiating element for the phased array. This antenna exhibits an impedance bandwidth of return loss below −10 dB across the frequency range of 24.8–40.3 GHz (47.6%), which represents one of the broadest operating bands reported for PCB-based, co-apertured, and dual-polarized end-fire antennas. Experimental validation of the fabricated phased array demonstrated that the two orthogonal polarizations could achieve beam-scanning ranges exceeding 90° and 60° at 28 and 38 GHz, respectively. The measured effective isotropic radiated power values exhibited distinct frequency selectivities between the two bands. To the best of our knowledge, this is the first demonstration of a D³ phased array that presents a promising solution for beyond fifth-generation (B5G) and sixth-generation (6G) millimeter-wave multistandard systems.