Many iPhone 8 users after upgrading to latest iOS 11.2.1 are facing issue with Spotlight search. The spotlight is not showing result for contacts. However it was working before the upgrade. Seems like something has broken the feature in new iOS release by Apple in iOS 11.2.1.
User tried to reboot the device but seems like it does fix spotlight issue for a while but will come back after sometime. Not all iPhone 8/7 users are reporting the issue but is reported by many users.
There are few workaround that you may try to fix the Spotlight issue in iPhone on iOS 11:
Solution 1: Reset Spotlight preference
Shut down all the spotlight switches in Preferences/General/Spotlight. (Settings → General →Spotlight Search → SEARCH RESULTS). Then hard restart the phone. Toggle on only the contact switch in spotlight. Wait for a few minutes and all the contacts must appear now. Later, you can enable other searches if you want.
Reset all contacts. Go to ->Contacts App, click on Groups and choose to ‘hide all contacts’ then switch back to ‘show all contacts’.