Disable WIFI order with keychain access
I had the exact same problem, and I found this solution to work pretty well for me: By creating a profile that you install into your iPhone, you ensure that only the iPhone will know about the guest network.

Here are the instructions:


Install the official "Apple Configurator app" on your Mac-Book: https://itunes.apple.com/app/apple-configurator-2/id1037126344
Create a new Profile: Go to File -> New Profile -> Wifi -> Configure
Enter the name (SSID), password and security settings for the guest network. You may want to check the Auto Join option.
Save the profile File -> Save...


Now delete references to the Guest network from both your Mac and your phone.


Finally connect your iPhone to your Mac and install the newly created profile into your iPhone. File -> New Window -> Select your phone -> Click the green + icon -> Profiles


Now only your iPhone will have knowledge of the guest network and your MacBook will never try to connect to it.

It's also working well in the other direction: Once connected to the Guest network through the profile, my phone will never try to connect to my enterprise network even if it's saved in the keychain. Although I can't explain why .. but this seem to do the trick !