how can i capture the traffic of my iphone

See this question.

I also (accidently) posted this to the old thread which is linked above:

Maybe you can use your router to capture it.
Not all routers support this, but e.g. AVMs FritzBoxes support this.
On the FritzBox web interface you can activate the capture
which creates a download of the capture file which you can open with Wireshark.
As long you don't close the website, the capture will go on.
But you will capture all network traffic, maybe from other devices in your network.
So better inform the other users or build up an independet network only with your router, PC and iPhone.