iOS can throw a warning message if there is water in the USB port during charging. Electricity and water are famously spicy friends.
Their recommendation is just to tap the bottom of the phone to get the water out, let it sit and dry for a few minutes, or use a Qi charger if you absolutely have to charge with a wet USB C port.
Most phones, including Apple’s, are pretty water proof these days. Rice is only going to get rice dust in your speaker, mic, and charge holes. Just tap the water out of let it sit for a few minutes.