It's a scam.
However, it sounds as though there's stuff on his phone that shouldn't be there, or he wouldn't be worried about it. So he probably needs to delete some things and never do whatever it is he is so scared about having evidence of coming out. The best case is that it's a few photos of himself, he's over 18 and he's not sending them to anybody. The worst is that he's a child or that the photos/video are of something illegal.
You need to talk to him and find out.
But it's still a scam - one that relies upon people having a guilty conscience/fear of being found out - but a scam all the same.