This is on Windows 7 and happens every day if I don’t start the Xamarin Bonjour service before Visual Studio and opening a Xamarin.iOS project. It’s not that big a deal but something must be switching the Xamarin Bonjour Service from Automatic. I set it to automatic a few times but it gets reset to Manual. Once it’s running it stays running for the rest of the day.
If you get this make sure the Bonjour Service is running. If it’s not, open the services MMC. You can do this from Task Manager but make sure on the Processes tab you click the Show processes from all users button as the service may not start. Then on the services Tab in Task Manager, at the bottom right then when the Services MMC opens scroll to the bottom. If you don’t see Started then right click on the service and click Start.
Hopefully you should be able to select iPhone 6.1 in the combo box and all will be well. If not see this tip on Visual Studio to Mac Connectivity.