Multiple select form with checkboxes

You group multiple checkboxes using the name option.

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox

<fieldset>
  <legend>Choose your interests</legend>
  <div>
    <input type="checkbox" id="coding" name="interest" value="coding" checked>
    <label for="coding">Coding</label>
  </div>
  <div>
    <input type="checkbox" id="music" name="interest" value="music">
    <label for="music">Music</label>
  </div>
</fieldset>

It seems like that’s how phoenix do it but within a schema list look up (e.g. name="user[famous]").

https://hexdocs.pm/phoenix_html/Phoenix.HTML.Form.html#checkbox/3

<input checked="checked" id="user_famous" name="user[famous]" type="checkbox" value="true">

If you have a lot of checkboxes, I would suggest you use multiple_select from phoenix.