Fixing Xcode 9 issue: "iPhone is busy: Preparing debugger support for iPhone"
There are multiple solutions for this:
Solution 1: Patiently wait for 10 to 15 minutes. Have a tea or roam around ;-)
Solution 2: Disconnect device from the system. Restart both iPhone and Xcode and then rebuild again.
Solution 3:
Go to Windows → Devices and Simulators (Shortcut key: cmd+shift+2)
You’ll see iPhone device connected to system with message
iPhone is busy: Preparing debugger support for iPhone
Click on plus button (+) present in bottom-left corner.
This will show the device connected to system. Click on Next button.
Thereafter you’ll see ‘device setup was successful’. Click on Done button.
Solution 3 worked for me!
Solution 4:
Unpair your device and then pair it again. Thereafter follow Step 3.