SecretBox does not save your secrets on the internet. This means that when you get a new phone, your secrets stay with the old phone.
Secrets are saved in "secretbox" directory on your sdcard (media card).
To move secrets to new phone, simply back them up from your old phone to PC (see the FAQ regarding backup) and then copy them from PC to your sdcard on your new phone.
Alternatively, you may want to simply take the sdcard out from the old phone and put it in the new phone and be done with it.