macOS sierra not recognized iphone

Welcome to the Apple Support Communities!

I understand you have a Mac computer with macOS Sierra and your iPhone is not being recognized in iTunes. The resource below provides some troubleshooting steps for this issue:
If iTunes doesn‘t recognize your iPhone, iPad, or iPod

When iTunes on your computer doesn't recognize your connected device, you might see an unknown error or an "0xE" error. If you do, follow these steps and try to connect your device again after each step:

1. Make sure that you have the latest version of iTunes that works with your computer.

2. Check that you have the latest software on your Mac or Windows PC.
3. Make sure that your device is turned on.
4. If you see a Trust this Computer alert, unlock your device and tap Trust.
5. Unplug all USB accessories from your computer except for your device. Try each USB port to see if one works. Then try a different Apple USB cable.
6. Restart your computer and iPhone, iPad, or iPod.
7. Try connecting your device to another computer. If you have the same issue on another computer, contact Apple Support.

If you use a Mac

1. Hold down the Option key, click the Apple menu, and choose System Information or System Report.
2. From the list on the left, select USB.
3. If you see your iPhone, iPad, or iPod under USB Device Tree, uninstall third-party security software. If not, contact Apple Support.