Well, it's claimed to be based on a true story. But like many such claims, some creative liberties might have been taken to make it more engaging for the audience.
Well, without more specific information, it's hard to say precisely. However, generally speaking, it could be about an event where the act of not answering the phone was crucial. For example, it could be a story of a person who was being harassed over the phone, and by not picking up, they were able to start taking steps to end the harassment. Or it could be related to a crime investigation where the suspect was trying to contact someone, and that person's decision not to pick up the phone played a significant role in the outcome of the investigation.