White cap holds the phone in that hand (his left) to make the call. In the phone call picture, there doesn’t appear to be anything wrong with that hand.
In at least one of the still pics that Fox shows, white hat guy’s RIGHT arm is messed up. The hand looks very fake.
He may have had to use his gimp hand to use the phone. People can do that, though I'm sure it's not easy. The other side of his body had the bag with the bomb.
If you look at all the others, you'll see he holds it in the same place all the time. It's position never changes. It's always bent.
In the picture where he's leaving, right after the explosion, you can see there's something odd about his shoulder, and the length of his arm - and it's STILL bent.