where is my phone back up is stored

For iTunes backups :

Mac:~/Library/Application Support/MobileSync/Backup/

The "~" represents your Home folder. If you don't see Library in your Home folder, hold Option and click the Go menu.

Windows Vista, Windows 7, and Windows 8:\Users\(username)\AppData\Roaming\Apple Computer\MobileSync\Backup\

To quickly access the AppData folder, click Start. In the search bar, type %appdata%, then press Return.

Windows XP:\Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\

To quickly access the Application Data folder, click Start, then choose Run. In the search bar, type %appdata%, then click OK.

You are unlikely to be able to make much, if any, sense of the files in that folder, unless you restore to the backup