Which phone number for TCR Registration

We have a Spectrum Business Connect phone number that is absolutely never dialed. It is my understanding (I didn’t set it up) that this line is ”pointed to” our company main phone number 972–304-1800 that is managed by RingCentral. With RingCentral we have this 972-304-1800 number forwarding all calls to the owner’s cell phone exclusively. Business phone 972-304-1800 cannot accept text messages nor the number assigned to us by Spectrum. Everything actually comes to and from a cell phone managed by a third party. We practically never text with a customer or vendor - it is an odd occurrence if ever done. Do we need to register? Which number do we register?