Remove the speaker enclosure from the iPhone.

Before re-fastening the speaker enclosure to the inner frame, be sure the four small EMI fingers rest below the lip of the LCD frame.

Before reassembly, be sure to clean all metal-to-metal contact points between the EMI fingers and the internal frame as well as the brass screw mounting point with a de-greaser such as Windex. The oils on your fingers have the potential to cause wireless interference issues.