Make use of your Breadcrumbs in your phone-specific views, to give a simple page title and navigation up 1 in the Breadcrumb stack. You have already configured every page with Breadcrumbs, so use them in your phone view header.

phone_breadcrumbs_builder.rb

# lib/phone_breadcrumbs_builder.rb
# inspired by https://gist.githubusercontent.com/marlosirapuan/3ceb02972400ea98ac5c8f419a61806b/raw/d994dc2d6b35702b4a66e2d1a01a9e9956883375/bulma_breadcrumbs_builder.rb
#
# Make use of your Breadcrumbs in your phone-specific views, to give a simple page title and navigation up 1
# in the Breadcrumb stack. You have already configured every page with Breadcrumbs, so use them in your phone view header.
#
# Example render in your phone view header:
#
#   `<a href="/"><i class="fa fa-chevron-left"></i></a> This Page Title`
#
#
# You can use it in a view by passing it to the `:builder` option on `render_breadcrumbs`:
#
#   <% if request.variant == [:phone] %>
#     <%= render_breadcrumbs builder: ::PhoneBreadcrumbsBuilder %>
#   <% end %>
#
# You will need to place this class in a location that is loaded by Rails. One
# suggested is `lib/phone_breadcrumbs_builder.rb`. You may need to adjust
# Rails' load path in `config/application.rb`:
#
#   config.eager_load_paths << Rails.root.join('lib')
#
#
class PhoneBreadcrumbsBuilder < BreadcrumbsOnRails::Breadcrumbs::Builder

  def render
    ret = []
    ret << render_back_element( @elements[-2] )
    ret << render_element( @elements[-1] )
    ret.join(" ")
  end

  def render_back_element( element )
    return nil unless element && !element.path.blank?
    content = @context.link_to_unless_current( show_arrow_back, compute_path(element), element.options)
    if @options[:tag]
      @context.content_tag(@options[:tag], content)
    else
      ERB::Util.h(content)
    end
  end

  def render_element( element )
    return nil unless element
    if element.path == nil
      content = compute_name(element)
    else
      content = @context.link_to_unless_current( compute_name(element),
                                                 compute_path(element),
                                                 element.options )
    end
    if @options[:tag]
      @context.content_tag(@options[:tag], content)
    else
      ERB::Util.h(content)
    end
  end

  # font-awesome back button
  def show_arrow_back
    "<i class='fa fa-chevron-left'></i>".html_safe
  end

end