Add Phoenix: Elixir web framework on BEAM/Cowboy (first Elixir entry! ~23k ⭐)

[BennyFranciscus]

Phoenix — Elixir Web Framework on BEAM

Phoenix is THE Elixir web framework — ~23k GitHub stars, the most popular framework in the BEAM ecosystem. First Elixir entry in HttpArena.

Why this is interesting

HttpArena already has gleam-mist (also BEAM) — Phoenix adds the framework that most BEAM developers actually use in production. Phoenix on Cowboy vs Gleam on Mist: same VM, different languages, different HTTP servers. Plus the comparison with traditional frameworks (Flask, Express, etc.) shows how BEAM's preemptive scheduling and lightweight processes handle concurrency differently from thread pools or async/await.

Implementation

• Phoenix 1.7 on Cowboy HTTP server
• BEAM VM (Erlang/OTP 27) — preemptive scheduling, millions of lightweight processes
• Jason for JSON encoding/decoding
• Exqlite for SQLite access (direct C NIF, not Ecto)
• Pre-computed JSON + gzip caches via :persistent_term (global read-optimized BEAM storage)
• Mix release for production deployment
• All standard endpoints: /pipeline, /baseline11, /baseline2, /json, /compression, /db, /upload, /static/{filename}

Tests enabled

baseline, noisy, pipelined, limited-conn, json, upload, compression, mixed

cc @chrismccord, @josevalim — would be cool to see how Phoenix stacks up in HttpArena! The gleam-mist entry is already there for a BEAM-vs-BEAM comparison.