If I am an employee of a business and prepare the business tax returns as part of my job responsibilities, am I required to obtain a PTIN

No. An employee who prepares his employer’s federal tax returns as part of their job responsibilities is not required to sign as a paid preparer. Accordingly, unless the employee prepares other federal tax returns for compensation, he or she is not required to register and obtain a PTIN.

Sources:
Publication 947 (2/2018)
§ 6109. Identifying numbers
IRM Part 4. Examining Process. Chapter 11. Examining Officers Guide (EOG). Section 51. Return Preparer Program