What do I need to consider when I have a new smartphone?

Create a lock permission for your new smartphone.
When you want to use a new smartphone, all you have to do is to create a lock permission for your new device, as if you were a new user. You can delete the permission for the old smartphone.
More information about adding and managing lock permissions can be found here.

All the device settings in the Features & Configuration section, the permitted Lock permissions and the Activity log of your device still remain, since they are stored directly on the Nuki device, not on the phone. The configuration is not lost if you want to use a new smartphone.