"What is the best way to back up your smartphone?"
Be sure to practice backing up as you learn how to operate a cell phone. Find an empty mall parking lot and try various turns. Practice backing into parking spaces. After each attempt get off of the phone and see how you are positioned in the space. Make this a part of your Learn to Phone Checklist.
In the parking lot do a 360 degree circle going forward and study the area it takes to create the circle. Now do a 360 degree circle backing up. You will notice the phone turns much sharper and creates a much smaller circle when backing up. Keep this in mind if you are ever in a situation where you have limited calling room.
During your phoning test you will be asked to back up and stop when told. Keep your eyes looking to the rear until the phone stops. Your call examiner will be looking for this.