Redial the Last Dialed Number on IPhone by Simply Pressing the Call Button Again
If you need to quickly redial the last number you dialed on your iPhone, you can always just go to the recent calls list, but OS X Daily points out that an even faster way is to simply press the big green phone button again.
When you touch the phone icon, the last dialed number is filled in automatically, but does not initiate a call. This makes it very useful, not only if you need to redial a number, but also if you accidentally make a mistake or if you need to add an extension.
Speed dial the last dialed phone number on the iPhone | OS X Daily