It depends on the type of plan, you need to be careful and understand the difference.
If you have a Roth account in a 401k or 403b, that is not an IRA, and you are not making IRA contributions. Employer plans are not IRAs even though they have a similar purpose; they are controlled by different laws and regulations. All your contributions (employee and employer match) are reported automatically on your W-2 and nowhere else. You do not enter them separately.
However, some small employers may participate in a "Payroll deduction IRA." This is a simpler option for the employer than creating a qualified retirement account. In this case, you directly own the IRA, and contributions may be made by your employer, but they are counted as coming from you. These follow the rules for IRAs, not 401k or 403b plans. If you have a payroll deduction IRA, then you treat all the contributions as if they were made by you. You must report them, they are not reported automatically on your W-2.
https://www.irs.gov/retirement-plans/plan-sponsor/payroll-deduction-ira
