Only after a day, I discovered a better way to use codex from my iPhone: use the Moshi app to connect into my computer via the Tailscale network. It is simpler, faster, and more secure than Agentboard.
GPT 5.3 Codex Spark has been released and it is super fast — much faster than the regular 5.3 codex. This will be good enough for, say, fixing the “must-fix” items quickly after a code review.