backing up iphone

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

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).

Back it up using iTunes instead of iCloud.

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.