Getting ancestors for manually set parent in template
As @Robin Schambach said, you need to loop through the ancestors.

{% set parent = craft.entries.section('pages').slug('phone-directory') %}
{% for ancestor in parent.getAncestors() %}
    {{ ancestor.title }}
{% endfor %}


This won't output the Phone Directory entry since you're just looping through its ancestors. So to complete the breadcrumbs you'll need to add 
{{ parent.title }} after the loop.