"I plugged my iPhone 6 in the computer via USB cable and launch iTunes manually, but there is no phone icon in the Device panel in iTunes. How can I make iTunes detect and recognize my iPhone 6?"
This is quite a troublesome, since we use iTunes to upgrade OS system, sync and transfer data, back up files etc. Don't be frustrated if this situation happens to you. There are a few steps for you to fix iPhone unrecognized by iTunes issue. Check them out in the following article.
Step 1 Restart both iTunes program and you iPhone, then, check the connection between iOS device and the computer. If there is no "Trust This Computer" note popping up, your USB cable may be not working. Try another USB socket or port and see if that helps.
Step 2 Check to make sure you've downloaded all required updates for your computer. Uninstall the old version of iTunes, download and set up the latest one on your PC or Mac. Connect iPhone to the computer, unlock the device and tap "Trust" in the pop-up window to build the connection.
Step 3 iOS devices require Apple Mobile Device Support, which should be automatically installed with iTunes. If it's not installed, it may affect the iPhone/iPad/iPod recognition by iTunes. To verify whether it is installed, follow the steps below.
Windows 8: Move the cursor to the upper-right corner and click the magnifying glass. Type Control Panel and hit Return. Click Uninstall a program. Apple Mobile Device Support will be visible in the list.
Windows 7: Start > Control Panel > Uninstall a Program, Apple Mobile Device Support will be in the list of currently installed programs.
If it is there, go back to the desktop. Press Win+R keys at the same time to launch run prompt and type "services.msc". When found Apple Mobile Device in the Services windows, select it and hit the "Restart" button.
Provided you've done all the troubleshooting solutions, your iPhone 6/6s, iPad Pro or iPod touch is still not recognized by iTunes, try to connect your iOS device with another computer. This can figure out it's a problem with the original computer or the iDevice itself. For sake of data security, you should back up your iPhone/iPad/iPod data beforehand.