The LTE network on Verizon Wireless is a GSM network. The CDMA networkffor VZW is being shutdown by the end of 2019. Verizon Wireless has recently required all phones activated on the network be capable of VoLTE/Advanced Calling meaning calls go over the LTE network.
If you want a pure GSM network, AT&T and T-Mobile are GSM networks.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.