The Displacement of an Object Oscillating on a Spring Is $\omega$

The displacement of an object oscillating on a spring is given by x(t) = x_mcos( $\omega$ t + $\phi$ ) . If the initial displacement is zero and the initial velocity is in the negative x direction, then the phase constant $\phi$ is:

A) 0
B) $\pi$ /2 radians
C) $\pi$ radians
D) 3 $\pi$ /2 radians
E) 2 $\pi$ radians