Have you checked to see if there is a volume limit being used on your phone? Look under settings -- music to see if it's been turned on. It's possible that if it's on that may be why your voicemails aren't sounding as loud as you expect. If it's not on and you suspect something is wrong with your earpiece you may want to visit your local Apple Store if possible (or Verizon if necessar) to have them check it out. Does it sound low when on speaker also?
If you feel that it's possibly a defect you should do as suggested and go to your local Apple Store if available. I always advise going through Apple for warranty issues if your device is still under warranty as yours clearly would be. Assuming you haven't had any water damage (yes, I know the iPhone 7 is water resistant so this is a little less likely) or any other type of damage then it's possible it's a defect. If you have anyone else around that has the same device ask them to test theirs out to see if it sounds louder than yours. If not it's possible that the volume is just lower than you expected and it's not deemed a defect but you'll never know unless you contact Apple. Another option if you don't have an Apple Store nearby you can call Apple. They can tell you if there are any Apple authorized repair facilities in your area that would be able to diagnose. And of cours, dealing with Verizon is an option
Maybe use another phone and leave yourself a voicemail and see how you sound. If it's still a problem compared to another iPhone, make an Apple genius appointment and seek resolution.
THOMAS BIENVENU- The new iPhone 7 has great sound and volume options. I apologize that your iPhone 7 is having volume issues. Time to pump up the volume and get you listening to your voice mails. Are you dialing *86 send to listen to your voice mails? Please go to Settings>Accessibility. Scroll down and see if phone noise cancellation is on (Green) Is Mono Audio on (Green)? Is the round switch in between L and R? Do you experience the same sound issue when you make or receive calls?
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