Over the years I've come up wit a number of ways to trace the network traffic from and two a smartphone for various purposes. So far they all had in common that the setup took some time, effort and in some cases bulk hardware. So in quite a number of cases I shied away from taking a trace as the setup just took to long. But now I've come up with a hardware solution for Wi-Fi tracing that isn't bulky and set-up in 60 seconds.
Earlier this year I bought an Edimax USB powered Wi-Fi mini access point that I have since used many times to distribute hotel and office Wi-Fi networks to my devices. Apart from being small it's easy to configure and ready in less than a minute after being plugged into the USB port for power. To trace the exchange of data with a smartphone it only needs to be connected via Ethernet to the Ethernet port of my notebook that is connected to the Internet via another network interface, e.g. its own Wi-Fi card. In addition, the Internet sharing has to be activated for the Ethernet port of the PC. This is supported in Windows and also in Ubuntu in the network configuration settings.
Once done, Wireshark can be used to monitor all traffic over the Ethernet interface. If the smartphone is the only device served by the mini access point, only its traffic traverses the Ethernet interface and from there the Wi-Fi while the notebook's traffic goes directly to the notebook's Wi-Fi adapter. That means no special filtering of any sort is required to isolate data flowing to and from the smartphone. The figure on the left shows the setup. Super easy and super quick to setup.