How can I find out if and how much I owe iTunes with my iPhone?j

You can see if you owe iTunes by trying to download something (including redownloading past purchases and new free items), you should get a 'problem with a previous purchase' message, and you can view the last 90 days purchases on your account on your phone via http://reportaproblem.apple.com - but you can only see how much that you actually owe via a computer's iTunes as per the instructions on the page that you posted from.

Sorry for my bump up this thread, now I have same problem with notice from iTunes. So, I'm following link of King_Penguin and need help from Apple Support to remove all of apps I don't need to use for now. So, could you please let me know how many days Apple will support me?

Thank a lot!

You can contact iTunes Support for as long as you want, there isn't a time limit or a cost for doing so. If you owe iTunes money then you will need to pay that off before you can download anything else from the store (including free items, redownloading past purchases, and downloading updates to apps). If you want to contact iTunes Support : http://www.apple.com/support/itunes/contact/

If you want to hide apps from the cloud for redownloading (you can't permanently delete them) then you can do so via your computer's iTunes : Hide and unhide purchases in iTunes or iBooks on your Mac or PC - Apple Support (when you hover your mouse pointer over an app the 'x' might not show on its top left corner, there's a bug in iTunes, but clicking there should still hide the app)