This is a heads up for an issue that was driving me batty. I finally realized that after the recent update to android 9.0 that problems I was having with making calls on my cell phone as well as calls on my home phone (which happens to be Vonage) were related. It turns out that after the update, something happened that caused all outgoing calls on either my Verizon wireless phone or my Vonage home phone to be able to place calls, but I could not hear any audio when it did. After replacing the Vonage adapter and Replacing my note 8, the problem was still there. While setting up the new replacement phone, it was showing me pop-ups of how to use various features, including the Wi-Fi calling. That was the ah-ha moment! I went into the settings and disable wifi calling, and all of a sudden everything worked properly.
I can't tell you why they interfered with one another. All I can tell you is what I did to remedy the issue. Hopefully this will help others that might be having the same issue.