Backing up a faulty iPhone

Hi I need to backup my iPhone 5S onto my mac, however I've smashed the screen of my iPhone. The phone still turns on and functions, but it's smashed badly to the point where the touchscreen no longer works. When I try to sync my phone to my mac it asks me to select 'trust' this device on my iPhone, which I can't select because of the smashed screen. Is there another way to back up my phone without actually needing to touch the screen on it?