Define phase at time $t$ and initial phase.

(N/A) The displacement of a particle executing Simple Harmonic Motion $(SHM)$ is given by the equation $x(t) = A \sin(\omega t + \phi)$.
$1$. Phase at time $t$: The argument $(\omega t + \phi)$ of the sine function is called the phase at time $t$. It represents the state of oscillation of the particle at any instant $t$,specifying both its position and the direction of its motion.
$2$. Initial phase (or Epoch): The constant $\phi$ is called the initial phase or epoch. It represents the phase of the particle at $t = 0$. It determines the starting position and the direction of motion of the particle at the beginning of the observation.