Is my contribution to my 403b plan through work the same thing as a traditional IRA?

A 403(b) plan is not an IRA.  Enter amounts shown in box 12 of your W-2 only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax.

As stated, 403(b) plans are not the same thing as a traditional IRA. However, contributions to your 403(b) may decrease your taxable income similarly to a traditional IRA contribution, as contributions are taken out of salary & wages pre-tax. For tax year 2024, taxpayers could contribute up to $23,000 to a 403(b). In some cases, taxpayers may be able to make nondeductible contributions to these plans. See the link below for more information.

Are 403(b) Contributions Tax Deductible?