You can try the following solutions:
1. Activate the small button at the top left of your iPhone, which cuts or resets the sound. Maybe it's just that, a fake move and your iPhone has gone silent.
2. Go to Settings> Sounds and turn off Silent mode if it is enabled.
3. Go to Settings> General> Accessibility> Assistive Touch
Once the Assistive Touch is engaged, a small round white-gray strolls on your screen. Select it, it displays a menu.
On this menu, touch the Device choice. Another menu opens, with which you can manage the sound. If it is cut, reactivate it.
You can then deactivate the Assistive Touch.
4. Last resort: restart your iPhone, by pressing the Home key and the Power key simultaneously.
If none of these solutions work, sorry, go to your nearest iPhone repair shop ...
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