There’s a neat little trick that I learned by accident when messing with my phone. It’s like redial, but not exactly. Basically, if you go into the Phone app and tap on Keypad and then press the Call button, it will automatically load up the last number you called.
Then just press the Call button again and it’ll call that number. So not automatic redial but partial. Don’t use it all the time, but it comes in handy sometimes.
"iPhone Tip – Partial Redial"
Reference : online-tech-tips.com