Hi Pravchaw:
Conversations are hard. If you want to chit-chat, try not asking such loaded questions. I do not struggle with addiction, but I would probably answer similar to your son to the examples of questions you gave above because the underlying goal of the questions is to "get in my case."
If you are wanting to discuss a heavy topic like the concerns you have for your son, still don't ask questions but instead try making just statements. "I see you have lost 2 phones in the last 3 months." Then just wait. If he responds, say something like, "Oh."
Hang in there. It does not seem like a complete cut-off is necessary, but timing and phrasing are everything.