Appropriate punishment?

My step son went to a friend's house after saying they would be at his Gigi's house without telling anyone. His mom called his phone, panicking but for some reason his phone couldn't receive calls. We thought his phone was dead because of that. He didn't use their phone to let anyone know anything. Mom wants to give him a firm but fair punishment. Son HATES reading and is normally glued to his phone. She suggests he be confined to his room until he reads a multi chapter book, and write a summary about it. I suggested that, or make him write sentences. Something similar to "I will not go anywhere without permission, and a charged phone." Also, explain that the phone as well as going places is a privilege, not a right and can be taken away temporarily. Opinions?