Found site using for PHN field in RA1000 Folders EXAM1 Folder Format in CATool.
CATool shows Folder Format EXAM1 has PHN mapped to work_phone_nbr:51 field.
This field in RA1000 creates a worklist column that is searchable by users in RA1000.
WFM may be configured to display a column for Patient Phone Number.
However in WFM this only presents as a column on worklists.
There is not an option to Search for within WFM via the column, a Quick search, or under Advanced search.