Multiphase flows with deformable interfaces are ubiquitous in nature and industry. Their dynamics depend on the precise location of phase interfaces, motivating interface-resolved simulations. Among various methods developed for this purpose (Mirjalili2017), phase field techniques have emerged as particularly attractive options, owing to their simplicity, parallel efficiency, regularity, and cost-efficiency. Most multiphase flow simulations based on phase field formulations have focused on the Cahn–Hilliard (CH) equation, largely because it has an associated free-energy functional and admits energy laws that promote numerical stability. However, the CH equation also presents several well-known challenges, including the need to solve a fourth-order PDE, unphysical coarsening, artificial shrinkage, and the lack of bounded solutions. These limitations have motivated the development of alternative conservative, second-order phase field models based on the Allen–Cahn equation. The (locally) conservative Allen–Cahn (CAC) equation, first derived by (Chiu2011), circumvents many of the difficulties associated with the CH formulation and has gained popularity for interface-resolved simulations. Nevertheless, unlike classical phase field models, the CAC equation is not a gradient flow of any known free-energy functional. As a result, achieving robustness, conservation, and physical consistency in multiphase flow simulations based on the CAC equation requires careful and systematic treatment, especially when coupling the phase field dynamics to additional transport processes and multiphysics effects. In this talk, we present an overview of our efforts to address these challenges. First, we demonstrate that, with an appropriate choice of model parameters, the phase field variable remains bounded. We then discuss how the phase field equation can be consistently coupled to other transport equations. Specifically, we introduce consistent formulations for (i) momentum transport, yielding a two-phase flow model that discretely conserves kinetic energy in the absence of viscous and capillary effects (for the first time in the field) and (ii) scalar transport in two-phase flows, including heat, species, and surfactant dynamics. Finally, we present an extension of the two-phase formulation to general N-phase systems (N>2). The presentation concludes with a discussion of the remaining open challenges associated with the CAC framework and directions for future research.