Based on the existing answers and the question, it appears that there is currently no way to get the seedphrase for a social login Kukai account. However, the team is working on a solution to give users the ability to export their private key as a keystore file as a backup. They are also looking into a more comprehensive multi factor for social wallets. The timeline for the keystore backup file is expected to be late December. It is important to keep an eye out for any changes to the timeline as well as any new solutions that the team may be working on.