To set up an iPhone and configue it to synchronize data to and from ownCloud server, go to the AppStore, search ownCloud and install the application. You will need to have an iTunes account to pay for the download. The price is 1,09€.
Once connected you can setup an application pin to protect your data in case your iPhone is stolen or lost, and allow the camera to upload the photos you take directly to the ownCloud server.
Select the configured account and begin using the app. By default, no data is passed locally to the iPhone, so the files you see in it are in the server. Selecting individual files gives you different options.