Several users have reported that all or some of their contacts disappeared after iOS update. If you consistently encounter this issue, try the following steps to resolve your issue. Here is how to recover lost contacts on an iPhone:
Note: Before trying these tips, please upgrade your iPhone to the latest iOS firmware.
iCloud stores your contact information. You may sync your contact info only if you had enabled iCloud Sync with Contacts enabled before losing your contacts (Settings > iCloud > Contacts). (How To Set Up iCloud)
You can log into icloud.com with your account and verify that your contacts are there on iCloud. Once you have verified that your contacts are intact on your iCloud, please proceed with the steps below.
Tap Settings > iCloud > Contacts and turn off your Contacts and turn back on. This will trigger a re-sync with iCloud to get your contacts back.
If asked, choose Delete from My iPhone when turning iCloud contacts off. Your contacts are already stored in the iCloud so you don’t need to worry. By triggering the re-sync, your iPhone will be loaded with all the contacts from iCloud.
Import from SIM
If you are storing contacts in your SIM card, then you may try this option:
Settings > Mail, Contacts, Calendars > Import SIM Contacts
Connect your iPhone to iTunes and sync your contacts.