The development of PHOEBE (phoebe-project.org) in the 2.0 through 2.2 releases has focused entirely on the forward model — creating synthetic models of light curve and radial velocity curves of eclipsing binary systems. The recent 2.3 release turns this focus towards addressing the inverse problem with the goal of determining the best parameter values and uncertainties in the model to represent observations. This includes a general framework for defining and manipulating parameter distributions, access to several supported forward modeling codes besides PHOEBE itself, the inclusion of gaussian processes, as well as built-in estimation, optimization, and sampling algorithms.