The party called can only hear at a very quiet volume because the microphone is too low.
A Jabra Engage 65/75 headset is used.
The microphone boom is not directly by the mouth.
The headset uses a noise cancellation function that affects the quality of speech when the microphone boom is poorly positioned.
Check if the dial tone switch, microphone position, and microphone volume are configured correctly.
Make a test call to test your intelligibility and speech quality with suitable volume by changing the position of the microphone.