Contacts.app
Background
Your iPhone stores the personal (and business) information in the "Contacts" app.
(For clarity, we will call this "Contacts.app".)
What is a "unified contact"
Contacts.app will attempt to identify people that appear in multiple stores, and display them as a single contact.
https://support.apple.com/guide/iphone/hide-duplicate-contacts-iph2ab28320d/13.0/ios/13.0
https://support.apple.com/guide/iphone/hide-duplicate-contacts-iph2ab28320d/12.0/ios/12.0
Where is the original data?
Most contacts come from another source in the cloud, like iCloud's Contacts or Gmail's Contacts.
Contacts.app makes a local copy of each contact, so that you can use the information when you are offline.