The ringer is set to its loudest perhaps it sounds really low

Hello!

Can you confirm that the ringer volume is very low even when your iPhone is lying on a table across the room, or just when you're holding it and looking at it?

Please go to: Settings > Accessibility > Face ID & Attention. Now, make sure the Attention Aware Features switch is turned off. Does that help? That feature will silence alarms, calls, etc. when it senses you are looking at the iPhone. (But it will not silence them completely. You will still be able to hear them faintly.)

Also make sure that Do Not Disturb isn't enabled, which wouldn't let your iPhone ring at all.

See: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support

Have a great day!