The answer depends on how you plan to model the PLL. If you are using a phase domain model, you can generate and plot the transfer functions with Spectre. If you are using a voltage domain model, you may want to try SpectreRF of some other RF simulator. You could also try to simulate an impulse response and then take the Fourier transform to get the transfer function but that would be very tricky.

How do you plan to model the PLL?