Phase boundaries can only exist if space is quantised, and there is no evidence, only speculation, that things like causal set theory have any reality. My view is that General Relativity is EXACT, and space is continuous. The effort to quantise gravity to make it mesh with quantum mechanics is misguided, as GR is fine as is and QM needs no modification to account for gravitational influence. Both GR and QM are very nearly pure mathematics, where the theory comes from taking a general case, namely all possible curvatures and stress energy for GR, and noting some contractions and symmetries that make the general case into the theory we have. What needs to change is the "standard model" which is known to be incomplete, and rife with adjustable parameters. In GR there are only two, the value of G and the value of the cosmological constant, which Occam's razor cannot cut down any farther.