Try a hard reset (make sure you data is backed up) and see if the clears up the issues you're seeing.
You might try disabling some features. Cortana has been known to tax some systems. I know it's not what antibody wants to hear - turning off smartphone features on their smartphone - but it may make the phone usable until a suitable replacement (hint: Surface Phone) is released.
Thanks for the suggestions. I went back to Verizon where they determined the phone was not working and replaced it. Now all is well.