Comment 4 for bug 678454

Currently if you choose "Upgrade Ubuntu", "Reinstall Ubuntu", or "Erase Ubuntu and reinstall", the new installation uses the same disks and partitions as the old one, so the resize step does not appear. I think this is correct behavior -- if you want to use a different disk and/or partitions, you can choose "Erase everything and (re)install Ubuntu" or "Something else".

The resize screen would also serve as a confirmation of what you're about to do. But there's no reason this particular choice needs confirmation more than others, and confirmation in general is bug 995335.