You can try plugging in any USB device. Keyboard, mouse, speakers/headphone, flash drive gizmo, whatever. If the port works then the port works and the problem must be the specific iPhone (or whatever) USB device you've been having problems with instead.
If this port is serviced by chipset add-ons (ASMedia, etc) then you might simply have a driver issue. Try uninstall/reinstall the drivers again (downloaded fresh from your mobo page) in case Windows somehow broke them. Don't forget to restart Windows (twice) if you want to ensure changes persist.
ASUS motherboards are installed by the end-user, they don't have any tamperproof stickers or whatever ... as far as the mobo box goes I don't know because I never bought that mobo, but I can say that every other ASUS mobo (or ASUS monitor) I've ever purchased has had very obvious and very secure ASUS-factory seals on the packaging, it's impossible to not notice if it's already been opened.
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