How do I enable Personal Hotspot in the OS X WiFi menu?
The Mac and iPhone need to have the same iCloud account set up.
If they do, and it's still not visible remove the account from and re-configure it on the device that's behaving unexpectedly.
I have been trying to fix hotspot on my wifes iPhone 6 and MBA, it would not work most of the time. I noticed the difference on mine that I had a hotspot section like above, where hers had her phone in the regular wifi section. Signing out of iCloud on the mac and signing in again fixed it.