Start by cleaning the earpiece grille very thoroughly with a soft brush. If that doesn't work, your next step is to seek a hardware repair from a professional. Given the age of the iPhone 12, a trusted third-party repair shop is often the most cost-effective solution.

I should explain the issue clearly in two categories: hardware vs software. The hardware causes are more likely given the symptoms, but we should still cover basic software troubleshooting first since it's easy and free. The user might not be technically inclined, so I'll avoid overly complex jargon. I'll list the troubleshooting steps in a logical order, starting with the simplest solutions (cleaning, restarting) before moving to more involved ones (resetting settings, hardware repair). I should emphasize that this is a known issue with iPhone 12 and mention the audio IC problem specifically, as that's a common hardware flaw in this model. The repair cost range and Apple's flat rate will help set expectations. The conclusion should reinforce that this is likely hardware-related and professional repair is the probable solution, while still guiding them through all possible self-fixes first.