Backup of a cracked screen
In case you have previously synced your iPhone to iTunes, it should automatically sync your device (with 'Sync' button). If you did that on the different computer, try connecting to it. After sync, restore the device from the previous backup in the recovery mode.

See also the following steps depends on your circumstances:


How to unlock your iPhone passcode if you have previously synced your iPhone to iTunes
How to unlock your iPhone passcode if you have never synced your iPhone to iTunes
How to unlock your iPhone passcode if you don’t have access to a computer