The 31-year-old WALK THE LINE star overturned his car on a canyon road above Sunset Boulevard in Hollywood after his brakes failed and he collided with another vehicle.
Phoenix was saved because he was wearing his seat-belt, but has revealed he was helped from the wreckage by the 63-year-old, who has a home nearby.
The actor says, "I remember this knocking on the passenger window. There was this German voice saying, 'Just relax.' There's the airbag, I can't see and I'm saying, 'I'm fine. I am relaxed. Finally, I rolled down the window and this head pops inside. And he said, 'No, you're not.'
"And suddenly I said to myself, 'That's Werner Herzog!' There's something so calming and beautiful about Werner Herzog's voice. I felt completely fine and safe. I climbed out. I got out of the car and I said, 'Thank you,' and he was gone."