Double contact two different phone numbers

I guess you are referring to Duplicate Contacts.

You may have stored the same contacts in multiple email accounts.

Either remove the contacts from the rarely used email account or disable contacts from the rarely used mail account in the iOS Mail app.

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

1. Is this your corporate/organization/enterprise/School Management iPhone? Then please contact the system administrator of your corporate//organisation/enterprise/School Management
2. If it is your device, in that case, do you have any profile installed by your corporate/organization/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Please contact the system administrator of the organization who provided the profile to you