In my area, there are a lot of areas where Verizon's LTE signal is noticeably "not as strong" as their 1x/3G signal. i.e. LTE will show 1-2 bars, but 1x will show 5 bars.
Now that you've flipped your voice calls to go over LTE, if you start noticing them dropping more, that may be why. They don't currently have handoff, meaning if you're on a VoLTE voice call, and lose LTE, it won't automatically switch your call back to 1x. The call will drop. You can disable VoLTE in that proves to be a problem.
But to your original question, it is normal for a Verizon/Sprint phone (not on VoLTE) to switch over to 1x to make a voice call, and then switch back to LTE when you're done.