Plotting of Phase drift in two input signals

Hi everyone, I have two signals (which are of Sinusoid form), each of them stored in an array in my Matlab Work Space. And when I plot Signal1 against Signal 2 (plot(t, signal1, t, signal2)) , I see that the phase between the two signals are not constant. The phase keeps drifting some times. So, I'd like to know which signal is not maintaining the constant phase. Is it the Signal1? or Signal2? or both? I'm not sure.

Is there a way to plot my signals so that I can see the phase drift locations in the graph. Also, in the same graph, the frequency of the signals may not be constant.So, is there a way to show the frequency at different points?

I think, I need to an FFT or some other process. But, I'm not quiet familiar with that process. If someone could please give me an idea about what I need to do to achieve my goal, that would be a really great help.

Thank You