If you use iCloud to back up your contacts, you can quickly bring them down to a new iPhone or iPad in a matter of seconds. There have also been reports of contacts mysteriously disappearing completely, which may require you to push them back down from iCloud again. Regardless of the situation, you can restore contacts from your latest iCloud backup in just a few taps.
How to re-download contacts from iCloud to your iPhone or iPad
Launch the Settings 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. If you've recently had contacts disappearing from your iPhone or iPad that you know you previously had, this could potentially solve the problem. If it doesn't, you can also try one other fix for disappearing contacts via the link below.