Ideally the card should be formatted in the phone and not on the computer. Have you tried formatting the card while inserted in the phone? Unallocated space means the space is not allocated (ready) for use. Normally, you can right click on the drive (disk) in disk management and choose to initialize and format the disk. If the phone has a USB connection and you have the USB cable you could try connecting via the USB cable instead of removing the card.