You can use created_at in Ecto/phoenix app with timestamps/1. When migrating data from a rails application to a phoenix application you will have many tables with a created_at column.
defmodule Phoenix.Accounts.User do
use Ecto.Schema
import Ecto.Changeset
schema "users" do
field :email, :string
field :password, :string, virtual: true, redact: true
field :hashed_password, :string, redact: true
field :confirmed_at, :utc_datetime
timestamps(inserted_at: :created_at, type: :utc_datetime)
end
end