Navigate to Settings/Apps/Advanced/Default Apps/Digital Assistant, then change from Voice to Google speech recognition. That should replace the mic symbol with the phone symbol.
You could try denying the Google app's mic permission or both.
Just wanted to add an answer that's a variant of guttermonk's for one particular use case: installing a certificate on a Bluestacks instance. At this writing the setting app for Bluestacks has been modified so that setting a pin or password is impossible, and so adding a user certificate is impossible also. But we can get a root certificate into the system ...