iPhone 12

Some things to check:

The ring/silent switch on the left side of the phone. See the following Apple article: How to put your iPhone on vibrate, ring, or silent mode - Apple Support

Check the ringer volume at Settings > Sounds & Haptics > Ringtone & Alert Volume.

Do Not Disturb. See: Use Do Not Disturb with Focus on your iPhone or iPad - Apple Support

If none of the above, also try restarting. See instructions in: Restart your iPhone - Apple Support

The most obvious thing to check is the Mute switch on the left side of the phone near the top. It should be toward the screen, and if you look at it you should not see an orange dot.

Next, check Do Not Disturb settings. Open the Control Center by dragging down from the battery icon. The button next to the word Focus is the DND switch to turn it on and off; it should not be highlighted.

Also, check the volume settings. With the Home screen displayed, the volume buttons on the side of the phone raise and lower volume. The bottom one is volume down, the one above it volume up.

If none of these resolve the problem post back; there’s more to investigate, but I didn’t want to clutter up an initial response.