Connect your iPhone to your Mac with a USB cable or use Wi-Fi syncing
Open Finder on your Mac
Select your iPhone from the Finder sidebar
Click the Info tab
Check Sync contacts onto your iPhone
Choose Contacts or a contacts group if available
Click Apply or Sync
On your iPhone, make sure Contacts syncing is enabled in iCloud if you use iCloud Contacts
On your Mac, open System Settings
Click your Apple ID
Click iCloud
Turn on Contacts
On your iPhone, open Settings
Tap your name
Tap iCloud
Turn on Contacts
If prompted, choose Merge
Open the Contacts app on your Mac to confirm the contacts are synced
If contacts do not appear, sign in with the same Apple ID on both devices
If needed, restart both devices and sync again