Now you're getting somewhere. Could be arp caching but seems unlikely. If you have Windows then install the Bonjour client.
If you had an iPhone (unlikely), it would probably just work fine. So I'll guess that you have an Android-based phone. Android calls this Network Service Discovery, for what it's worth. The only documentation I found was how to add the broadcasting side of this to an app rather than to verify whether or not the phone has the service toggled on or not.
That said, your phone can't discover network services unless you're connected to your local wi-fi network, right? And further, your phone needs to be connected to the same 2.4GHz network that your Raspi is connected to (rather than trying to route through your router which may not forward broadcasts like this).