In case the speaker on your phone is not producing any sound, then you should verify whether your phone is in headphone or Bluetooth mode. Unplug external devices and retest. Reboot your phone and upgrade to the software to exclude bugs. And finally a factory reset can also be tried (after data backup). When all these do not work, the speaker can be broken inside because of water or wear, and it is better to go to the certified professional for speaker repair or replace it.