I share an Apple ID with my mother's Apple phone, and sometimes I can see messages sent to my mother on the phone ... and the address book is shared. ..

Apple's mobile phone is calculated by ID. If you and your mother both use the same ID, it is normal to share the address book. If you want to cancel, the best way is to create your own ID, so that your mother's ID is different from yours. Because Apple says all its things are stored in the id. I used to have the same situation on the IPAD. After you create a new ID, it won't be like this.

Hope to adopt