First, as of October of last year, Strava no longer pairs directly with ANT+ or Bluetooth sensors. So you'll have to pair a different app with the sensors and then export the data files to Strava for analysis and display (I use Cyclemeter and have it set to automatically send ride data to Strava at the end of a ride)

Second, you don't pair the Duotrap using the Bluetooth utility for your phone - you pair it directly in the cycling app you want to use. For Cyclemeter, from the main screen you press the three dots at the bottom-right of the main screen to get to the "more" menu, then select "Devices" and press the "+ / Edit" button at the top right. Spin up the rear wheel to wake up the Duotrap sensor and it'll appear in Cyclemeter, ready to add. You can choose whether or not to use cadence data, and whether to use wheel speed sensor data all the time, none of the time, or "Indoors Only" (when the Cyclemeter app won't be receiving GPS data).