I assume you've been to the PS4 settings and selected add device?
Some routers can spoof the public IP address on your PS when putting them in the DMZ. For your phone it may look like the PlayStation is not in the same net.
You can check the IP address on your PS and on your phone, if they aren't in the same IP net try taking the PlayStation out of the DMZ (if it is).
Also make sure your phone is not using your mobile providers network, it has to get an IP address assigned by the WiFi of your router (and not accidentally connected to an open access point that isn't yours).
You're at the zoo, you have a popsicle. How can you be unhappy?
Nothing shows man's character more than by what they find ridiculous.
- Johann Wolfgang Von Goethe
I used to be cool.