I need advice, do I fess up?

I was at a festival and my best friend had his phone on the table. Before we left to the concert ground I grabbed his phone because he let me text someone on it and I was waiting for a reply. I forgot I had it ad it fell on the ground in the middle of the concert grounds. I'm sure its long gone and probably broken but he has no idea it was me that lost it. He also knows he did not take his phone off the table so everyone is looking for it in the camper. what do I do?! do I let everyone know I was the one who lost it or do I act oblivious? I feel sick about it.