This talk will discuss synergies between the Nancy Grace Roman Space Telescope and CMB lensing data to constrain dark energy and modified gravity scenarios. We will present a simulated likelihood analysis of the galaxy clustering and weak lensing data from the Roman Space Telescope High Latitude Survey combined with CMB lensing data from the Simons Observatory, marginalizing over important astrophysical effects and calibration uncertainties. We will discuss forecasted constraints on time variable dark energy, model-independent structure growth, Hu-Sawick f(R) gravity as well as a phenomenological model of modified gravity.