Where are my Minecraft worlds stored in Windows Phone 8.1?

[Windows Central Question]

I had a Windows Phone 8.1 device - HTC 8X - and then changed to another HTC 8X and restored my account. But I lost my Minecraft worlds. I want to upgrade to a newer phone soon, but I don't want to lose my Minecraft worlds again - how can I avoid that? The backup/restore function didn't save my minecraft worlds.
Thanks.

 

[ArtificiallyYours]

In the cloud.