why locally integrable g can't exist with schwartz function

Question

If $ \phi \in \mathbb{S}$, the space of Schwartz function, why there exists no locally integrable function $g \in \mathbb{R}^{d}$ such that $ \phi(0)= \int g \phi $ for all $ \phi \in \mathbb{S}$. Can someone provide some hint on it. Thank you.