If your iPhone is only showing Phone Numbers and not Contact Names, you can find below the steps to troubleshoot and fix the problem of Contact Names Missing on iPhone.
iPhone Showing Contacts As Numbers
If iPhone is not showing Contact Names, you will only be able to see Phone Numbers in Call Notifications on your device.
Similarly, when you receive a Message Notification, it will only contain the Phone Number and the Name of the sender will be missing in the Notification Message.
The problem of iPhone not showing Contact Names could be due to various reasons, ranging from iCloud Syncing issues to glitches in Contacts, Email or the Messages App.
1. Restart iPhone
The problem could be due to a stuck App or Service, preventing Contact Names from appearing on your device. This can be often fixed by restarting iPhone.
Go to Settings > General > scroll down and tap on Shut Down. On the next screen, use the Slider to power off iPhone.
After iPhone is completely powered OFF, wait for 30 seconds and press the Power button to Restart your device.
2. Edit Any Contact
Open the Contacts App on your iPhone and make a minor edit to any of your Contacts. This results in the Contacts database being refreshed, which should help in fixing the problem.
Open the Contacts App on your iPhone > tap on any Contact Name > On Contacts info screen, tap on the Edit option and make any small change.
You can make any small change like adding something in the Notes section and tap on Done.
This will refresh your Contacts database, which should help in fixing the problem of Contact Names Missing or Contact Names not appearing on iPhone.
3. Switch Contacts OFF/ON in iCloud
If your iPhone Contacts are being stored on iCloud, the problem could be due minor iCloud glitches or iCloud Contacts not properly syncing on your device.
Go to Settings > Apple ID Name > iCloud > move the toggle next to Contacts to OFF position.
On the confirmation pop-up, select Keep on My iPhone option. After the process is completed, enable iCloud Contacts back on your iPhone by moving the toggle to ON position.
On the next pop-up, select the Merge option.
Hopefully, this should bring back Contact Names back on your device.
4. Switch Contacts OFF/ON in Default Email Account
The problem could be due to your Email Contacts not properly syncing to iPhone.
Go to Settings > Mail > Accounts > select your default Email Account (Gmail, Hotmail, iCloud etc). On the next screen, move the slider next to Contacts to OFF position.
Wait for 30 seconds and move the slider next to Contacts to ON position.
5. Switch iMessages OFF/ON
Go to Settings > Messages > switch OFF iMessage.
After 30 seconds, move the toggle next to iMessages to ON position, to Enable iMessages back on your iPhone.
6. Signout from iPhone and Sign-in Back
Open Settings > tap on your Apple ID Name > scroll down to bottom of the screen and tap on the Sign out option.
On the pop-up, enter your Apple ID password > On the next pop-up, select/unselect the type of iCloud Data that you want to copy on your device and tap on Sign Out.
Sign back into your iCloud Account and you should now see both Contact Names and Phone Numbers.