A 401(k) plan is not an IRA. The amount you contributed is not included as income in box 1 of your W-2 form so you do not pay tax on it in the year you made the contribution.
In addition, you cannot take an IRA Deduction for contributions to any of the following plans:
- Roth IRA
- Section 457 plan
- SIMPLE plan
- Federal Thrift Savings Plan.
For General Guidelines on IRA Deductions: click here