For the clueless:

"The clue phone is ringing. It's for you."

And for the more theatrically inclined, a scenario:

You: Do you hear that ringing?
Clueless: No- what ringing?
You: Let me get it. (Mime picking up a phone.) Hello? Yes, he's right here. (Hand the invisible phone to Clueless)
Clueless: What's this?
You: It's the clue phone. It's for you.