Buried Alive

When the American contractor Paul (Ryan Reynolds) in Iraq woke up, he found darkness around him and nothing could be seen. After constant groping, I found a lighter, a knife and a mobile phone at hand, and it seemed that I was locked in a coffin and buried alive somewhere in the desert. He couldn't remember how he was locked up here. In this dark and small environment, Paul kept trying to contact the outside world, wondering what happened to him. As time passed, Paul finally figured out what had happened to him. However, the most critical situation at present is how to escape from the predicament. The only thing that can communicate with the outside world is a mobile phone, and the battery is running out. How to make reasonable use of this only thing? Paul finally used his mobile phone to contact the relevant departments of the US military, but he had no idea where he was. What should he do?