Plot phase shift over time

Hello, Is there an easy way to plot the phase shift between to signals over time ? the 'spectrogram' function seem to only plot the amplitude.

For now, i'm estimating the phase shift using the cross power spectral density ('cpsd'), but it gives bad results besause the phase shift of my two signals (both sinus at 1000Hz) change over time (for an unknown reason). I would like to plot the phase over time to understand why the phase shift is not constant as it should be.