iPhone 8+ Speakerphone Not Working

I recently purchased an iPhone 8+ and everything seems to be working fine with the exception of the speakerphone. For some reason, when I select speakerphone, nothing happens. The audio doesn't play through the speakerphone speakers or get any louder.

I did some research and played around with this a bit. The volume is all the way up. The ringer button is switched off of silent. I can play music and other audio that does play through the speakers. I'm up-to-date with my software (iOS 11.0.3).

Is this a carrier problem? My carrier is AT&T.

Has anyone else experienced this and been able to fix it?

Thank you for your help in advance.

Andrea