A photodetector that utilizes the phase-changing material Ge₂Sb₂Te₅ (GST) integrated with a silicon on insulator (SOI) waveguide is designed and analyzed in the wavelength (λ) range of 1500 to 1600 nm for telecommunication and optical fiber communication. The analysis of simulated structure reveal that GST is a promising material for photodetection applications due to phase-change property on a nanoscale, excellent absorption (with an absorption coefficient of ∼10⁶ cm ^{− 1}), lower bandgap of 0.63 eV in the amorphous phase, and 0.53 eV in the crystalline phase, tunability, and high phase stability. The photodetector structure consists of an SOI substrate, silicon waveguide, GST layer as phase changing material, and gold (Au) to make contacts. The photodetector’s optical and electrical parameters, such as electric field distribution of carrier generation rate (G), absorbed power (P_abs), dark current (I_dark), photocurrent (I_ph), and responsivity (R), are analyzed for both the amorphous (a-GST) and crystalline (c-GST) phases. The results demonstrate the potential of GST material to design high-performance photodetectors for various applications. The highest resistivity of 2.29 A / W is achieved for a-GST at λ = 1550 nm, with a bias voltage range of 0.5 to 2.5 V. The maximum absorption is observed in the amorphous phase as compared to the crystalline phase of GST. The calculated values of I_ph and I_dark are 0.24 mA and 78.54 μA for a-GST and 0.12 mA and 15.71 μA for c-GST, respectively. The optoelectrical behavior of GST-based photodetector on SOI waveguide demonstrates their potential application in photonic integrated circuits. Our work proposes an approach for using GST in photodetectors and analyzes both phases of GST that have not been explored before. Therefore, for the viability of the reported work, a detailed comparison is also presented with other simulated structures and found that the proposed device provided excellent results with low bias voltage.