Thanks. The issue with long term cold storage on an old phone seems to be not getting software updates when planning to keep it off line and so apps not working properly. 
Your idea makes more sense for sure. 🙏

cristaiji

bitcoin

Using an old phone as a cold storage device

You could use that old phone as part of a 2 of 3 multi sig wallet, just for backup in case you loose access to one of the other two signing devices.

Otherwise just use it for your regular spending, not for long terms cold storage.