If you have his father's phone, then it is a good idea to call his father. However, it is better if his parents know about the possibility of Bitcoin in his wallets. He should know what his son has. And at least you have shared the important information to his father as a friend. Regarding what will his father does, you must let him decide it. If he knows how to track the private keys and how to access the wallets, then you only need to share the information. But if his father doesn't know anything about the Bitcoin technology, you need to guide him, at least by sending some instructions or the like.