I had this same problem back when I had my Gen 1 Volt (so it has been a while ago). If I remember correctly, it was because my phone was set up to backup my contacts to the My Verizon cloud and for some reason there were two records of each contact on the cloud list. The phone did show that there were two cloud backups saved by showing 2 cloud icons in the contacts data in addition to a phone icon under a "Connected Via" tab.My wife has her IPhone paired to our 2016 Volt, and when we look at "contacts" for the phone on the Volt, my cell number (and home number) are in there twice under my name.
So if she tries the phone with voice commands, and says "call ALLAN Mobile" the response is, "Multiple mobile phones for ALLAN" and we can't figure out a way to tell the car which one to use.
Any ideas? Is it maybe downloading favorites AND also the rest of the contacts from the IPhone? It doesn't seem to be possible to delete one of the numbers from the Volt's contact list
The fix was to go to the My Verizon web site and manually edit the backed up list so that there was only one record of each contact. That deleted one of the cloud icons on the phone's list and fixed the double listing in my Volt.
I hope that I'm remembering this correctly, and if you are not on Verizon, I'm not sure how anyone else's phone cloud service works.