Possible causes for this issue:

• Phone might be in silent mode
• Phone ringtone might have been selected as ‘None’
• Phone volume could be set to lowest
• Issue with phone speaker
Troubleshooting:

• Check volume of your phone by going through following settings,  Menu >
  Device > Sound > Volume > Check Ringtone & notifications.
• Increase volume by dragging the slider halfway or full. You can also increase
  / decrease your ringtone and notification sound by pressing Upper / lower
   volume key.
• Go to Menu > Device > Sound > Phone ringtone and select any specific ringtone.
• If Ringtone is set as ‘None’, you cannot hear ringtone coming through.
• If still issue persists, factory reset your XP5 by following options:
  Menu > Setting > factory reset > reset phone > select erase everything.
• Back up all your contacts, messages, photos, videos etc before factory reseting
  the phone
 

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