2.4 and 5 GHz networks on the same router are always separate (you'd see a 2.4 and a 5 option to connect to) unless, for noise-reduction reasons, the router has disabled either of those connections. Now, when connected to the same router, unless they have been configured NOT to do so, devices should be able to 'see' each other, so in theory you should be able to connect to the phone even if it's on the 5GHz network.
If the camera, however, needs a direct connection to the phone or is somehow restricted to 2.4GHz somehow, you'd have to manually select the 2.4GHz network on your phone WiFi options (just like connecting to a different network, because they ARE different networks).