This thesis investigates the potential of gallium phosphide (GaP) as a platform for advanced integrated photonic devices, leveraging its exceptional optical properties. Significant advantages over traditional materials like silicon nitride (Si3N4) are offered by GaP in terms of both light confinement and nonlinear effects. A fabrication process for GaP wafers is presented, successfully reducing fabrication time and enabling wafer-scale processing, with possibilities for future scalability using advanced lithographic techniques. Record-low propagation losses in GaP waveguides, together with record-high quality factors in both large and small resonators are presented. Enhanced dispersion engineering capabilities are offered by photonic-crystal Fabry-Pérot resonators, especially when combined with the strong light confinement of GaP, allowing tailored dispersion profiles and high reflectivity over broad frequency ranges in compact devices. Notably, in these devices, the intrinsic losses of the resonator are independent of its dispersion, unlike in ring resonators. Dispersion profiles that are otherwise unattainable in conventional ring-type resonators are presented, and, for the first time, dissipative Kerr soliton generation at room temperature in GaP is demonstrated, surpassing the bandwidth and footprint of similar devices made from Si3N4. Broadband optical parametric amplification with small-footprint GaP-based traveling-wave parametric amplifiers is demonstrated, exceeding the gain capabilities of similar Si3N4 devices and the bandwidth of traditional erbium doped fiber amplifiers, offering significant advantages in optical communication systems, providing large bandwidth, high gain, and low noise figures.