It sounds like the iPhone isn't detectable for AirDrop.
Check for these settings on the iPhone
- check that you are signed in to iCloud (Settings>iCloud)
- wifi on and connected to the same network as Mac
- Bluetooth on
- within 30 feet or so of computer
- Control Center- swipe from bottom of screen, tap AirDrop and make the phone discoverable by contacts or everyone
Give the Mac and phone a moment or two to see each other.
Hope this helps!