Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump under an increasing shear rate. Even though these fluids are single-phase suspensions including nano-sized particles in a carrier liquid, various additives have been included in the suspensions to form multi-phase shear thickening concept. Despite novel concepts in compositions, rheological models have been studied only for single-phase STFs until this time. In the present work, multi-phase suspensions were fabricated adding aluminum oxide particles in a nano-silica/PEG based STF. Additive amount and temperature were selected as variables in the rheological measurements. Upon obtaining experimental data from the rheological tests, viscosity curves of the multi-phase STFs were adapted for a phenomenological model which was suggested for single-phase STFs. According to the results, the model gave proper fitting for the flow curves beyond the thickening point. However, it yielded a lower performance to predict the shear thinning region prior to the thickening onset. Therefore, a modified model was developed to fully cover the rheological behavior of multi-phase STFs. By the modified model proposed in this study, flow prediction of multi-phase STFs was improved due to the enhanced fitting performance, especially in the shear thinning region.