$x = A \sin (\omega t +\phi)$ $....(1)$

$\frac{ dx }{ dt }= A \omega \cos (\omega t +\phi)$

acceleration $(a)=\frac{d^{2} x}{d t^{2}}$

$a=-\omega^{2} A \sin (\omega t+\phi)$

$a =\omega^{2} A \sin (\omega t +\phi+\pi)$$.....(2)$

from $(1) \;and\;(2),$ phase difference between displacement and acceleration is $\pi .$