How to see how I'm sharing phone data with

There is no way to determine who has the Passcode to your device, if you have given out your Passcode or think someone may know it, then change it now. Set a passcode on iPhone - Apple Support

• You can view who is signed into your account by going to Settings > [name on top], and scroll to the bottom to view devices that are signed in.
• You can use Safety Check to view information that you are sharing. How Safety Check on iPhone works to keep you safe - Apple Support

Unless you've given access to someone, no one has access to your phone.