In this paper, a high efficiency phased array antenna is introduced for fifthgeneration (5G) smartphones. The configuration of the design is achieved by employing eight insensitive L-ring/slot-loop resonatorss with linear array form on the top of the handset mainboard. The design exhibits high radiation performances even though the beam-steerable array is implemented on a lossy FR-4 material. The proposed design exhibit a frequency bandwidth of 18-20 GHz with a single resonance at 19 GHz. The designed antenna exhibits wide beam-steering, high efficiencies, and sufficient gain levels at 19 GHz of 5G communications. In addition, the proposed phased array design has sufficient radiation behavior in the adjacency of user-hand phantom. Moreover, its characteristics are insensitive for various substrate types.