No need of doing something like this. You can backup your 2-of-3 multisig seed phrase/private key and public key in this order in three different locations:

Seed 1, MPK 2
Seed 2, MPK 3
Seed 3, MPK 1

In this way, if you lose one backup, you will still be able to recover back your coins and there is not need for any fourth backup, especially in what is not recommended like phone.

Backup should be completely  offline.