Apply a suction cup to the back glass, as close to the center of the bottom edge as possible.

Pull up on the suction cup with strong, steady force to create a gap between the back glass and the frame.

Insert an opening pick into the gap.

Depending on the age of your phone, this may be difficult. If you're having trouble, apply more heat to the edge and try again.

If your back glass is badly cracked, covering it with a layer of clear packing tape may allow the suction cup to adhere. Alternatively, very strong tape may be used instead of the suction cup. If all else fails, you can superglue the suction cup to the broken back glass.