I realize this is probably too late, but this question go bumped onto my radar by a recent comments, so I will answer it here. If you are using specialized power systems, there is nothing you can do to use that block, however, you can use replacement blocks that provide the equivalent behavior. For instance, if you look at this model, it has behavioral versions of blocks that do work with phasor. The reality is, that for now, you cannot combine dc and ac circiut networks with specialized power systems in the same model (there are tricks with model references and code gen if it a must).
Please see this example and look at how they use simulink to interface with the phasor circuit. (you can right click and look under mask to see what is under blocks)
As an alternative, simscape now supports frequency based simulation, and is not restricted to a single frequency, so you could try using that instead of specialized power systems.