What should a son do upon discovering nude images of girls and boys on his father's phone, and can there truly be men of this nature?

The presence of objectionable images on a mobile phone is a cause of temptation, and they must be removed, as Allah Almighty says: "O Children of Adam, let not Satan tempt you as he removed your parents from Paradise" and "And do not follow the footsteps of Satan." It is not permissible to harbor ill-will towards others merely because these images are present, due to the possibility of the device being hacked, and as Allah Almighty says: "Avoid much of suspicion." The father should be advised wisely and compassionately regarding these images, while showing good faith in him. Furthermore, it is not permissible to inspect the devices of others without their explicit or customary permission, and one must beware of religiously forbidden espionage.