Tl;dr: Apparently Phoenix is an Erlang / Elixir thing, and something for those of us not on Erlang to pay no slight attention to.

It would have been better to put that in the first paragraph, or even the title, so we would not need to scroll past reams of breathless hype trying to discover any single thing that we might have some use for someday.

A million connections on one server is no great trick today. It's table stakes.