<p>Deep mixing (DM) is one of the most widely used techniques for treating soft soil roadbeds. Industrial by-products, such as phosphogypsum (PG), are often used as partial substitutes for cement (CM) to reduce carbon emissions. The potential application of PG in enhancing the performance of cement-soil deep mixing piles is experimentally investigated in this paper. A series of laboratory tests, including unconfined compressive strength (UCS) tests, uniaxial cyclic loading tests, hydraulic conductivity tests, and toxicity characteristic leaching potential (TCLP) tests, were conducted. The results indicate that the Atterberg limits were significantly affected by the increasing PG content, leading to an increase in both the plastic limit (P.L.) and liquid limit (L.L.) of the soil, while causing a decrease in the plasticity index (P.I.) value. The results of the mechanics test indicate that the uniaxial compressive strength (UCS) achieves its peak value when the PG/CM mass ratio is 20%, and subsequently decreases as the PG/CM mass ratio increases. The relationship between cumulative strain (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\varepsilon }_{p}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ε</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation>) and loading cycles (<i>N</i>) in solidified soil was found to conform to an empirical model, and the fitting parameters a, b, and c were successfully determined. The state of the <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\varepsilon }_{p}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ε</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation> vs. <i>N</i> curve can be determined based on criteria a, b, and c, and a clear discriminating standard is provided. The results of the permeability test indicate that when the mass ratio of PG/CM ranges from 0 to 20%, there is minimal variation in hydraulic conductivity coefficient. Nevertheless, as the mass ratio of PG/CM continues to increase, a significant rise in hydraulic conductivity coefficient was observed. Finally, the TCLP test shows that the incorporation of PG will not have an adverse impact on the environment. This research offers a novel perspective on the resource utilization of PG, highlighting its potential as an innovative solution in industrial waste management.</p>