- Store it offline on my iPhone ? Is it possible ? Encrypt it on my computer ?
Any thoughts ?
Smartphones are not suitable because its likely to be connected to internet at some point. Storing it any form digital form pose the risk.
As others said you should keep the seeds in offline format which can be on a piece of paper inside water and fireproof box or you can look for the secret ways like this one Securing Your Seed Phrase with Washers.
Duplicating a single key doesn't make sense because it would only result in having the same key in two locations. The best practice is to store the three keys at three separate locations where one has no connection or association with the others and is positioned far from the remaining two.