What to check

Remove the telephone cover and check the wire connected to the 'P' terminal is sound (outgoing speech).

Measure the voltage between 'P' (-) and 'F' (+), which should be at 6-12vDC.

If there is no voltage on the 'P' wire it would suggest it is open circuit either because of a poor termination or a break in the wire itself.

Check terminations in any junction that may be feeding this phone. It is possible the wire passes through another phone on the system.

Corrective Action

Ensure all connections are sound or consider substituting the wire with a spare.