A simple solution could be css-only. You can set styles in your stylesheet, and then adjust them on the bottom of it. Modern smartphones act like they are just 480px wide, while they are actually a lot more. The code to detect a smaller screen in css is
@media handheld, only screen and (max-width: 560px), only screen and (max-device-width: 480px) {
#hoofdcollumn {margin: 10px 5%; width:90%}
}
Hope this helps!