You're assuming that he and his dad have a good relationship and that they can actually contact the son who has no phone
they might even of just sent the email to the wrong adresss
Well I was guessing that as his dad checked with the son that the phone was missing, and then gave the description/offerer the p&p money that they were at least on speaking terms. Also, what's stopping the son contacting the phone then if the dad doesn't want to? Surely if he wants it back, he'd be able to just phone it and sort it out himself.
I guess it's possible the email went to the wrong address, but then if the heard nothing back, and want the phone, they'd just ring and ask what's going on.

I never knew such a form of fanboy existed!