iPhone calls are so soft I cannot hear the caller

You can adjust your volume on the side buttons while you are on a call or access the Control Center and use the slider with the Ear Symbol to scroll it to a higher volume. Here is a link to show how to access the Control Center: Access Control Center on your iPhone - Apple Support

Go to Watch app on your iPhone. Go to Sound & Haptics, Alert Volume is a slider. Even at Max volume I wish it was louder.