It's a peer to peer connection - either side can cause problems that show up in strange ways. We're not saying it's definitely the phone, but unless you've actually tried multiple phones with the same result then you can't conclude that it's not the phone.
Remove the battery from the phone to reset it, delete the phone from sync, do a fuse 29 reset on sync and re-pair it. If that doesn't work try a master reset. Then try another phone if it still doesn't work.