Question iphone caller can't hear verizon customer

[2hondochica]

My sister and her husband both got new Iphone 12s at christmas. Their carrier is spectrum and when either of them calls me (Verizon carrier non iphone) I can hear them but they cannot hear me. I always have to call them back, then they can hear me just fine. One of my sister's co-workers has a Verizon phone (not common in this area) and she can barely hear her coworker when sis initiates the call. they can hear the voicemail greeting and can leave me a voicemail, no problem. my phone is 4G - theirs are 5G. I also have an ATT carrier cell phone (4g I think) and they can call that phone and have no problem hearing me. ANY idea what might be going on? they have done all the updates. Neither of the carriers have been any help. Thanks!
Kelly