Revisit phone/contact management

When copying phone numbers over to our new field, I noticed that we need to:
* check that all current information is accurate. In particular, there is contact information entered that is listed by department name, but the contact information is 311. We should figure out a good flow for this or whether the information just needs to be updated
* I'm not sure if these incorrect contact segments are even used anywhere, which brings up another point; we might want a way to tell where a snippet or page might be currently used
* potentially check for duplicate phone numbers or other contact information while someone is creating or editing a new contact snippet, maybe using an autocomplete or generic chooser
* Let's make #2702 and #2039 friendly for content editors.