Of course you can throw more servers/caching/database locks, but the advantage of using Elixir & Phoenix is that you can do a lot more with less.
Think how much the code would be simpler and easier to reason about without caching.
Or reducing the numbers of servers you need from 150 to 2 and with better performance [1]
If I had to use OpenAI API I would pick my favorite HTTP client and just use the Rest API and write a small wrapper around it for my needs.