To determine the magnitude and phase response of any linear, time-invariant (LTI) system, you need to get the impulse response of the system in the time domain. This can be done by adding the "Discrete Impulse" block (DSP Sources Library) as the input to your filter system. The output of the system is then defined to be its impulse response.
After you have the impulse response, you want to take the FFT (Transforms Library), and separate the complex output of the FFT into the Magnitude and Phase components by the "Complex to Magnitude-Angle" block (Math Operations Library). You can then configure the outputs accordingly.
An example is attached to this solution.
