No way his dad wouldn't know if he lost his phone; it would be a major crisis. Same if it stopped working.
Ok but he went home after the trip into town, was tired, and was said to have gone right to sleep....so in that case he may of never even looked for it, or maybe thinking he left it in the truck and would get it in the am. Either that or the phone would of been really the only thing of value someone would want to hurt Dylan over, and it would of been used by now.