If someone attempts to add your phone to a family share group an invitation to join the group will appear on your phone. You must accept the invitation before you are added. So if you didn't receive an invitation or received one and didn't accept it you have not been added to a family share account.
You can also use the Find my iPhone app on your phone. Open it and all of the devices that are logged in to your Apple ID plus all of the devices in a family sharing group that you belong to (if any) will be shown in the app.