Every Facebook page you click on, group/ photo/subject you like, and friends you are tagged with, are stored in order to compile your interests.
However, if your only concern is still that Facebook is listening in on your conversations, here is how to turn off your mic:
On iPhone, go to Settings > Privacy > Microphone > Facebook. On Android, go to Settings > Apps > Facebook > Permissions > Disable microphone.
Read our full article on how to limit Facebook’s use of your data here.