My iPhone 12 keeps losing the contact names and just displays numbers

• Is this your corporate iPhone? Then please contact the system administrator of your corporate
• If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management? Then also, please contact the system administrator of your corporate/organisation/enterprise/School Management.
• Else, delete and add the mail account which hosts your contacts in the IOS mail app. It is a matter of 1-2 minutes only.

Unlike some Android devices, contacts are neither stored locally on an iPhone nor in SIM. They are synced to an email account that you had Google, iCloud, AOL, Exchange, Outlook, Yahoo or any Other

If Contacts on iCloud, try this --> Restore contacts, calendars, bookmarks, and more using ...