In order to accurately simulate violent free surface flows, such as breaking waves, it is essential to consider the effects of the gas phase including wind, bubbles and entrapped air pockets. This is key to accurately reproducing the behaviour of fluid flows often with strong gas-liquid interaction, including the pressures acting on nearby structures. However, the interfaces between the different phases can cause numerical instability, often resulting from significant density differences and leading to discontinuous fluid motion, such as splashing. To resolve this issue, this study presents a new multiphase boundary model that enables more accurate and stable simulations. This model uses the projection-based particle method (ISPH) [1], which solves a Pressure Poisson Equation (PPE). Instead of directly connecting target particles, the proposed model uses virtual particles to solve interparticle forces between different phases, thereby reducing the numerical error. These virtual particles are also incorporated into the PPE matrix, allowing the pressure fields of all phases to be solved within a single discretisation space, rather than using existing over-grid techniques [2]. The proposed model ensures stability without numerical stabilisers, e.g., artificial repulsive forces. The effectiveness of the proposed model is demonstrated through benchmarks targeting an oscillating droplet, two rising bubbles [3], and a dam break. The model reproduces the interphases sharply and stably, while producing smoothed pressure fields, even in the presence of breaking waves splashing gas and liquid particles. Since the simulations are driven by the CFL condition (αdt=0.1), fast and practical computations can be achieved.