If you need to get better sound from your smartphone in a room that is too big, we only have a trick to make it happen.
All you need to do is take any empty, clean and dry paper cup lying around your house and put your smartphone in it. That’s the whole trick, and it greatly amplifies the sound from your device.
If you don’t have a cup, or if your phone is too big, you can try a cup instead. Or a coffee mug. Or a glass cup. The bottom line is that you need some kind of container for the best sound direction (i.e. so that it doesn’t scatter in different directions).