I just read through the manual, and it looks like one of the devices (my guess is the laptop) is connected to the guest network, not the main one. Why do I think this? Because if you move the laptop to the cable then the phone can see the laptop, implying that the phone is on the main net.
Suggestion: disable guest networking completely then disconnect and reconnect both the phone and the PC.
BTW: that is quite a router. I am not sure I would want to connect a shared disc directly to the box that is connected to the internet. That triggers my paranoia a bit.
Good luck!