Geometric frustration is recognized to generate complex morphologies in self-assembling particu- late and molecular systems. In bulk states, frustrated drives structured arrays of topological defects. In the dilute limit, these systems have been shown to form a novel state of self-limiting assembly, in which the equilibrium size of multi-particle domains are finite and well-defined. In this article, we employ Monte Carlo simulations of a recently developed 2D lattice model of geometrically frus- trated assembly [1] to study the phase transitions between the self-limiting and defect bulk phase driven by two distinct mechanisms: (i) increasing concentration and (ii) decreasing temperature or frustration. The first transition is mediated by a concentration-driven percolation transition of self-limiting, worm-like domains into an intermediate heterogeneous network mesophase, which gradually fills in at high concentration to form a quasi-uniform defect bulk state. We find that the percolation threshold is weakly dependent on frustration and shifts to higher concentration as frus- tration is increased, but depends strongly on the ratio of cohesion to elastic stiffness in the model. The second transition takes place between self-limiting assembly at high-temperature/frustration and phase separation into a condensed bulk state at low temperature/frustration. We consider the competing influences that translational and conformational entropy have on the critical tem- perature/frustration and show that the self-limiting phase is stabilized at higher frustrations and temperatures than previously expected. Taken together, this understanding of the transition path- ways from self-limiting to bulk defect phases of frustrated assembly allows us to map the phase behavior of this 2D minimal model over the full range of concentration.