Save/Get ObservableCollection to/from Roaming

I'm making a Universal windows store app and I have an ObservableCollection.

What I want is to save the data from the ObservableCollection somewhere so that the data can sync between desktop and phone that have the same universal app, and then I need to be able to get this data so that I can update the ObservableCollection.

I haven't done anything like this before, so I'm not sure how to proceed... Do I need to save this to an XML file, and if so, how will I sync it between the different devices. The only storage methods I know how to use are:

     ApplicationData.Current.LocalSettings.Values["key"] = "something"; 
     //Which stores "something" in local storage with key "key".

     ApplicationData.Current.RoamingSettings.Values["key"] = "something";
     //Which stores "something" in user's  Microsoft account storage with key "key".

Last one I think looks like to what I actually want, but it wouldn't be practical to save all my ObservableCollection items and properties like this.