Hi JonClay,
Telephone, Mobile, Primary Email and Secondary Email
They should be the display names of the fields, if you can't search for them, it's probably because they have different display names in different forms.
You mentioned: even though they do appear on the Contact Form within Dynamics
The default form on the workflow depends on what you are choosing to use in the app:
For example:
(1)

(2)

So you can select the form have these four fields in dynamics,and refresh workflow dialog, then you should see them.