Phase of motion

I'm confused at this question and could use some help.

a body oscillates with simple harmonic motion along the x-axis. it's displacement varies with time according to the equation

A=A0sin (wt + PI/3

where w= pi radians per second, t is the seconds, and a0= 7.6m
What is the phas of the motion at t= 2.6s? answer in units of rad.

What is the definition (from your book) of "phase of motion"?

When you reply, please post a corrected version of the equation; there is currently an unmatched grouping symbol.

Thank you.

Eliz.

Sorry the problem was written A=Asin(wt+pi/3)

My book doesn't really define phase of motion it has harmonic motion, wave motion , equation of motion, but I don't actually see a definition.