How do I know if the plan I have is a 403(b) or not?

You could ask your employer, plan administrator or Voya what type of plan it is. A IRC 403(b) plan is specifically for public schools, certain tax-exempt organizations (those under Internal Revenue Code Section 501(c)(3)), and certain ministers. 

A 403(b) plan, also known as a tax-sheltered annuity plan.  It is a retirement savings plan primarily for employees of public schools, certain tax-exempt organizations, and ministers, similar to a 401(k) for private sector workers. Employees can defer part of their salary into their IRC 403(b) account. It will be tax-deferred until retirement. Your employer may also contribute to your IRC 403(b) plan.