For whatever reason, this requires quite a few manual steps, but here's why you want each because Verizon brands this HD Voice and you have to enable it on the Verizon site and then in the iPhone 6 or higher itself:
voLTE. This brilliant acronym (voice over LTE) let's you use voice and data on your Verizon phone. Because this is a CDMA phone, you can only have voice or data normally, but by using VOIP over the LTE data channel, this is solved. Unfortunately you need to do a few things manually:

• Go to the Verizonwireless.com site. Turn on HD Voice on your phone.
• Go to your iPhone 6 or later and choose Settings/Cellular/Cellular Data Options/Use LTE and pick Voice and Data.

Wifi Calling. This uses wifi if available for calling. It appears to check the quality of the wifi connection and sometimes use it, you can tell at the top if the status base says something like VZW Wifi instead of Verizon.

• Goto Verizonwireless.com for each phone you want to enable and turn on Wifi Calling. It will ask you for the emergency address. This is because with E911, the dispatchers need to know where to send the police 🙂
• Got to your iPhone and choose Settings/Phone/Wifi Calling and it also asks you for an address