Ringer too quiet
I do apologize for your issue with the quiet ringer. Especially if you have some important calls you are waiting for. Somethings to keep in mind. Everyday, you want to make sure you power down your cellular phone completely for about 10-20 seconds. That way it's refreshed.
Second, check your profile on the phone is on silent,meeting,outdoors,normal,etc? When you highlight either of them you can customize it. Make the volume higher. Also, for testing purposes set only factory made ringtones, which are already on your phone. Test them all out, and see which ones are sufficient. A lot of times if you download ringtones or use MP3's as ringtones, they are not loud enough.
I know this will assist you with your phone and ringers!