Hey there, and welcome to Apple Support Communities Drdtexan1,
From our understanding, you would like to stop your Yahoo email contacts syncing with your iPhone contacts. We can certainly understand your concern and can help provide some insight.
We would like to ask you a couple of questions in order to get a better understanding. First, what exact version of iOS are you currently using? We ask as the menus and options can change slightly between versions of iOS, and we want to make sure we provide the most accurate steps. You can locate this by going to Settings > General > About. Also, have you tried going to Settings > Mail > Accounts > Your Yahoo email > Contacts > and turning the Contact feature off? If not, go ahead and do so. Once you followed these steps you will be prompted that performing this action will remove all contacts associated with your email off your iPhone.
We thank you for your answers, they will help guide us to the next troubleshooting step.
Kindest regards!