In recent years, interest in improving the properties of polymers has become particularly important. Thermal stability is one of these properties that has been widely used in recent years due to its specific applications. One way to increase thermal stability is phosphorylation. Also, due to environmental concerns, a lot of attention is being paid to water-based latex. A Butyl Acrylate (BA)-silicone-acrylic copolymer was obtained by Mini-emulsion polymerization. Nuclear Magnetic Resonance (NMR) spectroscopy, Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), Differential Scanning Calorimetry (DSC), and ThermoGravimetric Analysis (TGA) analysis were used to characterize the goods thoroughly. DLS verified the presence of 80–100 nm-sized latex particles. DSC results revealed that the presence of silicone chains in the matrix, considering that silicone has a lower glass transition temperature than BA, reduces the matrix's glass transition temperature and increases the chains' flexibility. In addition, the presence of phosphorus in the copolymer chain increases the Tg. Formation of char for B5S5P3 due to the presence of phosphorus, causes a delay in the destruction of the sample and an increase in the temperature of the destruction of the matrix in TGA analysis. Also, the presence of silicon played a significant role in increasing thermal stability. Sample B5S5P3 with 30% phosphorus by mass showed first and second decomposition temperatures of 348 and 630 °C. In addition, in the flame analysis, the B5S5P3 sample showed the best combustion performance among other samples.