If your contacts disappear mysteriously or deleted anyhow, on your iPhone or iPad than you can quickly bring them back within seconds. You can restore contacts from your latest iCloud backup in just a few steps.
How to re-download contacts from iCloud to your iPhone or iPad:
- Launch the Setting app on your iPhone or iPad.
- Tap on iCloud.
- Turn On the option for Contacts - if it's already on, turn it off and then back on again to trigger a re-download. When asked what to do with existing contacts, choose the Delete option.
- If you are asked, choose to Merge contacts.
- Launch the Contacts app or the Phone app and verify your contacts are all there.
Keep in mind it may take a few minutes for all your contacts to come down.
For more information see here.