Hi @Ayse Jones
Is the phone in a case at all?
If so try removing it from the case and check if you can now be heard.
If not use a magnifying glass and a strong light to visually inspect the voice inlet hole on the bottom edge of the phone to see if it is blocked with lint etc.
If it is or you’re not sure, ''do not'' use a pin or probe to try and clear it as you may damage the internal microphone which is behind the hole. Try using a vacuum cleaner and see if this removes any obstruction.
If still no good then the phone will have to be opened and checked as there may be a problem with the internal microphone. There is another microphone in the phone which is used when using the phone in handsfree (loudspeaker) mode.