Blocking emails in iOS through either FaceTime or Phone Settings does not work.
Instead of using FaceTime blocking, I blocked through Call Blocking and Identification in Phone Settings.
I created a Contact labeled "A. Spam", to which I added a spammer's addresses from emails in my inbox.
This Contact was then added to Call Blocking (which states that FaceTime, Messages, and calls are blocked, but mentions nothing about emails).
Among the addresses under the "A. Spam", I including one of my own. I tested the setup by emailing myself. I received the email, so, it is evident that no email senders were blocked.
The only benefit to adding multiple spam senders to a Contact is that future emails from those addresses will be identified as "A. Spam", which will make junking them in iOS marginally easier.
NOTE: The "A." In "A. Spam" sorts the Spam contact to the top of my Contacts list for easy access upon selecting "Add to existing contact" in iOS Mail.