When you say "I want to make just one xaml page retrieving the information by the ID off my mysql table in the cloud", I'm tempted to interpret that as you wanting to go directly from your Windows 8 client to MySQL. You shouldn't do that for security reasons. You'll need to use your PHP layer in between. You may not have meant to imply that you'd go directly from the client to MySQL, but I thought I'd be extra clear about this.
I recommend creating a RESTful web service with CodeIgniter. Here's another question on StackOverflow which will give you some pointers:
Once you have a web service, you can easily talk to it from .NET using System.Net.Http.HttpClient. You can also very easily talk to a web service with JavaScript, so you may consider building your app using JS/HTML instead of .NET/XAML. The free book Programming Windows 8 Apps with HTML, CSS, and JavaScript by Kraig Brockschmidt is a good place to start.