Answer
Please see the work below.
Work Step by Step
We know that in an LCR circuit, the voltage and current are always at a phase difference of $\phi=+\frac{\pi}{2}$ or $-\frac{\pi}{2}$. At resonance, we have $X_L=X_C$. As the given frequency is lower than the frequency at resonance, therefore $X_L=(\omega L)\lt X_c=(\frac{1}{\omega C})$. We conclude that the capacitor dominates and hence the voltage lags behind the current and the phase angle is $-\frac{\pi}{2}$ or $-90^{\circ}$.
