In quest of effective materials and technologies for detecting toxic gas molecules, an attempt is made to detect phosgene gas molecule using MoS2 by employing dispersion corrected density functional theory calculations. Doping Si into the S-vacancy of MoS2 monolayer results in improvement of adsorption capability of phosgene gas molecule, reaching adsorption energy of -1.228eV. It is revealed that Si-doped MoS2 sheet is thermodynamically stable at high temperatures, and hence, room temperature stability is expected. Origin of interaction between phosgene and adsorbent is analyzed by calculating density of states, charge transfer, and vibrational frequency. Strong binding and more charge transfer modulate band gap and work function of the Si-doped MoS2 material post-phosgene adsorption indicate that such system is highly sensitive to phosgene. It is further shown that the sensing material is completely recovered by applying 0.6V/ magnitude vertical positive electric field. The reason for reduced stability of the system is revealed by variations in charge transfer process and induced dipole interaction due to the charge redistribution. The results suggest potential application of MoS2-based sheets for sensing phosgene gas molecule, where external electric field efficiently aids reversible adsorption process.