Moving to Millimeter-Wave (mm-Wave) bands would bring new challenges and certainly require careful consideration on the antenna designing for the fifth generation (5G) handheld devices. Compact antennas arranged as an array can be employed at different portions of a smartphone PCB to form linear phased arrays with high-gain and directional radiation beams. The focus of this manuscript is to propose a new phased array antenna design for 5G mobile platforms. Eight elements of compact Quasi-Yagi antennas are deployed on the top portion of smartphone PCB to form a beam-steerable phased array design. The -10 dB impedance-bandwidth of proposed 5G smartphone antenna spans from 25 GHz to 27 GHz providing 2 GHz bandwidth. A coax-to-microstripline with a truncated crown of vias around the coaxial cable has been used as a feeding mechanism for each radiation element. An Arlon Ad 350 substance with properties of ε=3.5, δ=0.003, and h=0.8 mm is chosen as the substrate of the 5G smartphone antenna. The phased array antenna has wide bandwidth, wide-scanning, high efficiency, and sufficient gain characteristics. In addition, the SAR function and radiation performance of the design in the presence of the human’s hand and head have been studied. The results validate the feasibility of the proposed design for use in the 5G handheld devices. Furthermore, using the presented Quasi-Yagi elements, the radiation properties of 2×2, 4×4, and 8×8 planar arrays are studied. The results show that the designed arrays (linear & planar) satisfy general requirements for use in 5G platforms.