With embedded ngspice you may do a small signal ac simulation. All result vectors may be plotted with their magnitude and phase.
If you want to exploit all the capabilities of ngspice, you have to invoke standard ngspice from within KiCad/Eeschema. A short introduction on this procedure is given in KiCad Eeschema as GUI for ngspice, tutorial for setting up the simulation . In addition to ac simulation standard ngspice allows multi-port S-parameter simulation. Magnitude/phase or real/imaginary may be plotted, polar and smith chart plots are available. The ngspice manual provides more information.