Explanation:
Displacement of SHM is
\(x = A\sin (\omega t + \phi )\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(1)\)
\(\frac{{dx}}{{dt}} = A\omega \cos (\omega t + \phi )\)
\(a = - {\omega ^2}A\sin (\omega t + \phi )\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(2)\)
\(a = {\omega ^2}A\sin (\omega t + \phi + \pi )\)
From (1) & (2), phase difference between displacement and accelertion is \(\pi\).