See these 0.13.x to 0.14.0 upgrade instructions to bring your existing apps up to speed.

• Enhancements
  • [Phoenix.HTML] Update to phoenix_html 1.1.0 which raises on missing assigns
  • [Controller] Add jsonp/2 for handling JSONP responses
  • [Channel] Enhance logging with join information
  • [Router] Add forward macro to forward a requests to a Plug, invoking the pipeline
• Javascript client enhancements
  • Add socket params to apply default, overridable params to all channel params.
  • Enchance logging
• Bug fixes
  • [Channel] Fix xdomain content type not being treated as JSON requests
• Javascript client backwords incompatible changes
  • logger option to Phoenix.Socket, now uses three arguments, ie: logger: (kind, msg, data) => { console.log(${kind}: ${msg}, data) }
• Backward incompatible changes
  • [Controller] plug :action is now called automatically
  • [Endpoint] The :format option in :render_errors has been renamed to :default_format
  • [PubSub.Redis] The Redis PubSub adapter has been extracted into its own project. If using redis, see the project's readme for instructions
  • [View] The default template web/templates/layout/application.html.eex has been renamed to app.html.eex