backing up iphone

You need to check what accounts you use on your iPhone to sync contacts. There are 3 possible sources:

• On My Device
• iCloud
• Other, non-Apple service (such as Google, Outlook, Yahoo, etc)

To backup contacts stored locally "On My Device", you can make iCloud Backup or backup on a Mac or PC. For instructions see: https://support.apple.com/en-us/HT203977

iOS Backup does not include contacts synced using over the air account such as iCloud:

https://support.apple.com/en-ie/HT207428

https://support.apple.com/en-us/HT204136

If you sync contacts via iCloud, you can export them all to vCard file using instructions found here: https://support.apple.com/en-ie/guide/icloud/mmfba748b2/icloud. If later, you need to restore contacts from vCard file to iCloud, follow instructions found here: https://support.apple.com/en-ie/guide/icloud/mmfba7399f/icloud.

If your contacts are synced from other non-Apple service, such as Google, Outlook, Yahoo or other, you need to check documentation provided by whomever supports your account how to backup/export contacts to a file (preferably vCard format as it is compatible with many services).

The contacts visible at iCloud.com are synced and not part of iCloud Backup. To turn on syncing from the iPhone, go to Settings > [username] > iCloud > Contacts.

If they don't sync, see: If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support

In addition to @QuickTimeKirk, some contacts are linked to other services like Outlook and Gmail. Make sure to sign in to other accounts on a new phone in Settings > Accounts&Passwords.

Back it up using iTunes instead of iCloud.