A Ge2Sb2Te5 (GST)-based microring resonator is designed and analyzed for optical switching-based applications. First, the optical properties of GST material having thicknesses of 130 to 230 nm on two commonly used substrates, i.e., silicon (Si) and silicon dioxide (SiO2), are investigated in detail. The phase-change property of GST plays an important role in tuning the resonant wavelength, absorption, and transmission loss in the ring resonator as its crystalline state has a higher refractive index (RI) compared with the amorphous state. Due to the phase-change property of the GST material, the effective RI of the waveguide core changes. A patch of GST is embedded on a ring resonator to optimize the response of light coupled in the ring and straight waveguide, that is tunable between its amorphous phase (a-GST) and crystalline (c-GST) phase. The difference in refractive indices between the two states of a phase-change material (PCM) renders it an optimal choice for the optical active devices used in light modulation and switching applications. The GST is employed as an active material in the proposed structure as it is significantly stable and results in reduced insertion loss (IL) compared with other PCMs. In the proposed design of the ring resonator, the finite-difference time-domain simulation demonstrates high extinction ratios of 16.05 and 20.50 dB at the THROUGH and DROP ports, respectively. Moreover, the low insertion losses (IL) of 0.33 dB at the THROUGH port in crystalline phase and 0.8 dB at the DROP port in amorphous phase, have been observed. The Q-factor of the ring resonator without a GST patch is 5.18×105, whereas with a GST patch, it is 5.13×105 and 1.28×105 in the amorphous and crystalline phases, respectively.