Sign in to the same Apple ID on both iPhone and Mac
On iPhone, open Settings
Tap your name
Tap iCloud
Turn on Contacts
On Mac, open System Settings
Click your name
Click iCloud
Turn on Contacts
Open the Contacts app on Mac
Check that the contacts appear and sync
Connect iPhone to Mac with a cable if needed
Open Finder on Mac
Select your iPhone
Trust the computer on iPhone if prompted
Sync contacts through iCloud.com if iCloud sync is not available
Make sure both devices are connected to Wi-Fi
Make sure both devices are using the latest software
Restart both devices if contacts do not appear
Confirm Contacts is enabled in iCloud account settings on both devices