You'll have to use Recovery Mode to go back to 9.0.2 and then update again if you wish:
- Make sure that you're using the latest version of iTunes.
- Turn off your iPhone and leave it off.
- Plug in your iPhone's USB cable to a computer with iTunes.
- Hold down the Home button on your iPhone as you connect the USB cable. Keep holding down the Home button until you see the Connect to iTunes screen.
- When you see this screen, release the Home button. If you don't try steps 2 through 4 again.
- When your iPhone is connected, iTunes will open. You'll see a message saying that iTunes has detected an iPhone in recovery mode.
- Accept iTunes's prompts to restore. Restoring in recovery mode will erase your iPhone, but it will now be back on iOS 9.0.2
Rather than risk a repeat occurence by updating OTA again, I suggest you download the 9.1b3 .ipsw from https://developer.apple.com/ios/download/ and use alt/shift+"Update" in iTunes.
The same thing exactly happened to me. https://twitter.com/mvxlr/status/649550081612353537
From what I can tell this seems like a bug in this beta.
Note that while the iPhone shows the screen as updating, the underlaying subsytem is still working. I can make Siri & Phone calls from my attached Watch for ex.
I wonder if there is any work around other then restore, which will cause data loss unforturnly because of bug #2 https://twitter.com/mvxlr/status/647015634438524929 i wouldn't want to loose my unbacked up photos