import android.media.MediaPlayer;
import android.media.AudioManager;

public class MyMediaPlayer {
    private MediaPlayer mMediaPlayer;
    private AudioManager mAudioManager;
    private boolean isPlayingOnSpeaker = false;

    // ... Other code ...

    // Inside your button click listener:
    mButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Get the application context
            Context context = getActivity().getBaseContext();

            // Initialize AudioManager
            mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
            mAudioManager.setMode(AudioManager.STREAM_MUSIC);

            // Toggle between internal speaker and earpiece
            if (isPlayingOnSpeaker) {
                mAudioManager.setSpeakerphoneOn(false);
                isPlayingOnSpeaker = false;
            } else {
                mAudioManager.setSpeakerphoneOn(true);
                isPlayingOnSpeaker = true;
            }
        }
    });
}