Here's another Nokia 6303 solution for not working microphone problem. The solution below provides the connection line paths and the components of the microphone circuit on Nokia 6303 classic.
The Nokia 6303 classic used a 5 pin digital microphne or DIGIMIC, just refer to the solution below to quickly locate it on the PCB board.
The solution above shows the conenction line paths of the MIC supply voltage, MICdata, MIC audio clock and ground pins, for easy tracing and check up procedure. You may start tracing each connection line paths, check all of the 100 ohms resistors, replace the digital microphone