The JobDesc field is unfortuantely not a field you can import data into via the contacts Table. This field is linked via the Entity table, and as such would require you to import directly into the Entity Table to populate data in this field.
This field is typically used to describe information regarding a Customer Job. For example, if you had a Customer named Jim, who you work with fairly often on a variety of different Projects that you wanted to keep separate, you would create a new Customer as a sub-customer of Jim for every new Project you did with him. On these sub-Customers, you would fill our the Job Information section to further specify What kind of work you are Doing for Jim.
It seems like what you are desctibing is the Contacts Job title at the company they work for is. I would recommend using the workaround that you described and creating a New field for this information.