Probably a lot depending on your workload. Here's a 2015 article about getting to 2 million concurrent connections[1] with Phoenix channels. They used a bigger rack space box, but it was 7 years ago and Phoenix and Elixir have both improved a lot here. Here's another example of someone hitting a laptop with 840,000 connections[2] on an intel mac with the following specs:

> 2.5 GHz Quad-Core Intel Core i7 16 GB 1600 MHz DDR3

Obviously memory starts to be a constraint for doing anything meaningful, but you can squeeze a lot out of 32gb of ram.

[1]https://phoenixframework.org/blog/the-road-to-2-million-webs...

[2]https://josephmate.github.io/2022-04-14-max-connections/