Phase change materials present a unique type of materials that drastically change their electrical and optical properties on the introduction of an external electrical or optical stimulus. Although these materials have been around for some decades, they have only recently been implemented for on-chip photonic applications. Since their reinvigoration a few years ago, on-chip devices based on phase change materials have been making a lot of progress, impacting many diverse applications at a very fast pace. At present, they are found in many interesting applications including switches and modulation; however, phase change materials are deemed most essential for next-generation low-power memory devices and neuromorphic computational platforms. This review seeks to highlight the progress thus far made in on-chip devices derived from phase change materials including memory devices, neuromorphic computing, switches, and modulators.