There are several reasons why someone may not be able to hear you on your Android phone during a call.
First, check if your microphone is not blocked or covered with a case or foreign object. Often, this is the simplest issue, and removing any obstructions can resolve the problem.
Secondly, ensure that your microphone is not muted. During a call, look for the microphone icon and tap on it to unmute if it's turned off.
Thirdly, check if the volume level is too low. Adjust the volume to the maximum using your phone's volume controls.
If none of these solutions solve the issue, then there may be an issue with your phone's hardware or software, and you should consider contacting the manufacturer or a technical support team for further assistance.