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Make sure the silent switch of your iPhone is not turned on. It is on the left side, above the volume buttons. If it is showing red, then switch it back. Red on it means it is muted. Then check if it is ringing now.
If that didn't work, then we can reset your iPhone and see if it works or not. Press and hold down the Power button and Home button (Volume down button instead of Home if using iPhone 7 or 7 Plus) at the same time until it shows the Apple logo. Then see if it ringing. (only reset if you know the code to unlock the screen of iPhone)
If that didn't work, then it must be some settings. So we can reset the settings. Go to Settings> General > Reset and tap Reset All Settings. This will reset ringtone settings, Wi-Fi, Bluetooth etc. You will have to connect to your Wi-Fi after resetting all settings.
Call from another phone and check if it is ringing now.
Please let me know if that didn't work, so we can continue troubleshooting.
Note : This is not my final answer. I strive to provide Excellent service or 5 star service. If you feel you've received anything less or if you are not satisfied or if my solutions didn't work, please don't rate me bad or poor or ok as it will badly affect my job here. Instead, please let me know and I will try my best to help you until you are fully satisfied or the issue is resolved.