You need to backup your iPhone to iCloud or iTunes. Once that is done, go to Settings>General>Reset>Erase All Content and Settings (that is, if you've already setup your iPad). After your iPad restores, you'll have the option to restore from iCloud/iTunes. There you can* pick your iPhone backup and begin the restore.
*Not 100 % sure iPhone backups can be restored onto iPads. I've read many threads on here that say it's possible, but I have yet to try it. If I were you, I'd backup the iPad first just to be safe.