Downloading iPhone Contacts via USB
Assuming you know his iCloud account details (which you will need anyway in order to remove the activation lock to give the iPhone to a new user) you can download the Contacts as a series of vCards directly from https://www.icloud.com/#contacts

Click the Gear icon bottom left, 'Select All', then 'Export vCard…' It will download a single file, called [First Contact Name] and [number] others.vcf
e.g. "Fred Smith and 27 others.vcf"
It will also try to import them immediately into Contacts on a Mac, but you can cancel that operation if that's not your desired result.