Q: I am trying to backup my broken iphone but can't get by passcode

If the screen is disabled and you cannot enter the passcode, you will not be able to create a backup. You will be forced to use the last backup that you created of the device on that computer or in iCloud. Nothing else that can be done.

Does your insurance not want you to return the broken device? Depending on the amount of damage to the screen, if you still have the old device, Apple may be able to replace the screen, however you would have to pay for that repair. It is possible, but they warn you it may not work, to just repair the screen and retain the content. However, they tell you not to count on saving the data. Apple cannot backup the device without being able to enter your passcode either. And even if you were to recover the backup, when you restored the new phone, everything you had done since the time you got it would be deleted and replaced by the old data. You do understand how a backup and restore function, correct?

See if this helps. There are several others available via search as well. About backups in iCloud and iTunes - Apple Support