The objective of this research is to utilize additive manufacturing (AM) techniques including 3D printing and inkjet printing, to create on-demand flexible packaging for high performance on-package phased arrays for 5G/mmWave wearable and conformal applications, in low cost, highly customizable and modular configurations. Towards the proposed research objective, different additively manufactured flexible dielectric and conductive materials have been characterized for their electrical and mechanical properties over the 5G/mmWave frequency band (26-40 GHz), and various inkjet-printed interconnects on 3D printed flexible substrates have been evaluated for their electrical and mechanical performance during a 10,000-time cyclic bending test over typical wearable flexible radii down to 1 inch. Then a proof-of-concept flexible on-package phased array with an integrated microfluidic cooling channel on 3D printed substrates has been fabricated and measured to demonstrate the multifunctional packaging. Additionally, a novel flexible and scalable tile-based phased array antenna has been implemented to achieve high volume communication for high frequency applications. Finally, an additively manufactured lens-loaded phased array design will be explored to enhance the performance of the traditional phased array with increased gain and broader steering range.