According to the ALM 12.53 installation document if you don't have your passphrase, then you will need to copy over the qcconfig file from the prior installation to get the passphrase. This is misleading somewhat as it appears to insinuate that the passphrase will be recoverable and seen during the installation. This thought is incorrect and the passphrase will be dragged along from the prior installation but will never be able to be seen or decrypted and thus is still unknown to the new admins. The only way to actually know what the passphrase is going forward is to install using an entirely new qcsiteadmin schema and choosing a new known passphrase and documenting it for the future so you do not end up with the same issue in future upgrades.
If you care to reuse the prior qcsiteadmin then you will need to follow the instructions documented within the installation/upgrade guide to carry forth this unknown passphrase by copying/migrating the qcconfig file that contains the encrypted phrase to the new system prior to performing the installation procedures as it needs to be there to be referenced since there is no way to decrypt or decipher it to know what it was. Documenting is the only way to know this passphrase in the future for upgrades and migrations and even the developers have no way of breaking this encryption. No amount of admin access or privileges matters in this issue as this encrypted passphrase is not visible to anyone at anytime (it used to be visible briefly during the versions prior to 11.52 (possibly changed in ALM 11) during the installation so it could be openly viewed during installation, but since that version they have masked the phrase during typing so it is no longer obtainable even during the rerunning of the wizard as it was in the past.
Hope this helps some, but unfortunately there is no way to obtain that phrase,