setting up personal cloud for backup

Hello lsteink.

Thank you for using Apple Support Communities. If you're looking to connect to local Network Attached Storage, you will need to use the Files app on your iOS device. For steps on how to use the Files app and how to connect to servers or external devices such as NAS, click here: Connect servers or external devices with Files on iPhone - Apple Support

Keep in mind that iCloud data such as backups are only stored on Apple's iCloud servers and not on NAS. For more details on how to create an iCloud backup, click here: How to back up your iPhone, iPad, and iPod touch with iCloud - Apple Support

For more information on iCloud, check out the resources below:

What does iCloud back up? - Apple Support

Introduction to iCloud - Apple Support

Get more help with iCloud - Apple Support

We hope this information is helpful. Cheers.