"I don't--" He still hasn't gotten a replacement phone. He keeps meaning to, but then there was Cas to deal with and then they were operating below the radar and dammit--wait. Wait, Cas has a cellphone. He starts digging through Cas' pockets in search of it. "Sorry about this, Cas. It's for a good cause, I swear. We'll get you an ambulance, get you patched up, get you well. It's gonna be okay. I promise, you're gonna be fine."

Honestly, he's reassuring himself more than he's reassuring Cas, because he cannot survive that loss a second time.