Best way to validate unique value on encrypted data?

Hello,

What is the best way to validate unique value on encrypted data column(e.g. Phone number)?

I found this thread ( https://forum.codeigniter.com/thread-67598.html ) But, I don't think it's correct way beacuase even if you add the same string you will get another value. 

What is the best way?

Please help me.

This: https://paragonie.com/blog/2017/05/build...hp-and-sql