How do I find out if someone has set up family sharing on my account because it wasn’t me
Why is family sharing on my phone
Go to Settings > [name on top] > Family Sharing, to see if it has been set up. To set up Family Sharing the request has to be approved on your phone, so someone would need to have physical access to your device and account to be able to accomplish that. It cannot be done remotely. If you feel your Apple ID has been compromised then follow these steps.
If you think your Apple ID has been compromised - Apple Support