You'll need to switch then. Verizon isn't going to carry or support the Passport. And VoLTE (Advanced Calling) has been around for a year or more.
The real question is not VoLTE (which has been active for nearly a year as noted by Snn5), but when Verizon is going to switch to allow LTE only phones and devices on their network with no legacy CDMA support. That is not the case now, nor have they said anything definite about when that will happen other than a very general eventually. The Passport is GSM and LTE only and has no CDMA support which is required at this time on Verizon. If you must have the Passport, I would not count on it being able to be used on Verizon's network in the next 12 to 18 months.