It is not directly incorporated into OpenStudio, but we model it in OpenStudio via an EnergyPlus measure that will add the PCM properties to a specifically named material (that is included in the intended constructions). This involves setting up an IDF file with all of the necessary MaterialProperty:PhaseChange objects defined that gets added to the translated OSM and has naming conventions that match what you set up in the associated materials in OpenStudio.
EnergyPlus documentation is here.
It is essential to pay attention to the note about setting HeatBalanceAlgorithm to ConductionFiniteDifference and having a larger (meaning shorter) timestep then you probably use normally. Both of those settings can be accessed through OpenStudio.