External processes

First, ISO 9001:2015 does not requires the use of job descriptions.

I use job descriptions in my work with organizations to describe for each role:

• Authorities;
• Responsibilities;
• Competence requirements. 

If the person handling the external service processes belongs to your organization, and your organization uses job descriptions, then you should use job descriptions. If that person belongs to another organization you can use work instructions, or standard operating procedures to fulfill the same purpose of a job description: stating authorities, responsibilities and competence requirements.

- How to document roles and responsibilities according to ISO 9001 - https://advisera.com/9001academy/blog/2018/02/26/how-to-document-roles-and-responsibilities-according-to-iso-9001/
- Enroll for free course - ISO 9001:2015 Foundations Course - https://advisera.com/training/iso-9001-foundations-course/
- Book - Discover ISO 9001:2015 Through Practical Examples - https://advisera.com/books/discover-iso-9001-2015-through-practical-examples/