Tap on the "cog icon" to go to the "settings" and tap on "Sort cards". On the following screen you can sort your cards alphabetically or customized. The way you decide to sort you cards also applies to the iPhone widget. If you chose to customize the order of your cards every card will be labelled with a "burger icon" on the right side. Tap and hold this symbol to drag the card to the position you prefer. Tap "save" in the top right corner.

Please read the FAQ "How can I enable the mobile-pocket widget?" for further information about using the iPhone widget.