The best tool I've found so far is MITMProxy [1]. It lets you snoop all your HTTP(s) traffic from your iPhone. You just have to keep it running on your PC (or server, if you want) and set the HTTP Proxy settings accordingly. Then you have to install a CA certificate (that has been locally created and is only known by you). It is pretty interesting what data your phone is sending. Of course, you could simply trick this tool by not using HTTPS (and send it over FTP or a custom protocol instead) but it is a good start.

[1] https://mitmproxy.org/