Your phone sounds could not be working because of something simple, or your phone needing a repair. First, check to see if your sound is up. Phones have multiple volumes for different things so be sure to turn up the right one or just turn up all of them to see which one is for what. Second, make sure sound is suppose to be playing. A lot of times, the phone will stop the sound if it needs time to buffer or if the app does not want to work. Give it time and try something else that you know plays sound like a ringtone. Third, if neither of those are right, then your speaker may be blown. Check out our troubleshooting page at HTC One M7 Troubleshooting for more help on your speaker being blown.