SIM slot or receiver broken?

Dropped phone water damaged (toilet)

Wasn't in very long.(dropped top end quarter of it)

Dried out in hot car. Tide line on phone....slowly disappeared but ever so faint now. All works. Expect SIM. So no calls txt etc.

Tried SIM in another phone SIM card works.

So what isn't working ?

Can it be fixed ? seems a shame when every thing else works....