SITUATION: you are on a conference call (using speaker phone) and they cannot hear you.
SOLUTION: on the top row of black buttons make sure you see "MIC" flashing on your display. Please see the manual in the link below for exactly where this MIC message should show up on your phone. Press the black button (technical term is "soft key") a couple of times until you see it flashing. The other party should now be able to hear you when you have your speaker phone enabled.