I solved this issue after continued research on the internet but after hours and hours of resetting and restoring the brand new modem as advised by the surfboard chat techs. I am not good at computers at all but do know enough to follow instructions if the correct ones are given. I kept saying to the techs I felt it was just something on the modem not clicked on (or off!) but that dialogue was ignored. Too long of a story so to cut to the chase for someone else who might have this issue with their new Arris modem:
Setup new modem and connected with my internet provider and everything worked and streamed just fine except calling over WiFi. Our house has a lot of trees in a rural area so we do not have cell phone service without WiFi. I knew it was the modem that was not allowing the calling over WiFi as I went to a neighbor’s home, was on their WiFi, and could make a call no problem. Thus, not my phone or my internet provider’s issue. Tech support ignored me when I told them this. What I finally found with an AI search assistant (not sure why it never came up earlier) was to check the IPSec, PPTP and L2TP settings in the modem’s firewall and make sure they were all checked. I knew how to get into my modem’s web interface because the techs did walk me through that so they did help me in that regard. I was already in my modem’s web interface so I went to advanced settings (I think, if I remember correctly) went into the firewall setting and found these settings and sure enough the IPSec box was not checked (the other two were). As soon and I clicked the IPSec box my phone could make calls over WiFi. One little checked box…sounds so simple if the surfboard techs had only known to tell me that. Frustrating to say the least as I had been chatting with them about my issue for hours. I was ready to unplug the modem and send it back and go back to my old one. I hope this helps someone else save some time.