All of this Gross amount (in box 1) is from a CSRS pension annuity.
The taxable portion is the difference between your box 1 income and your box 5 contributions.
Publication 721 (2024), Tax Guide to U.S. Civil Service Retirement Benefits states:
Part of the annuity benefits you receive is a tax-free recovery of your contributions to the CSRS or FERS. The rest of your annuity benefits are taxable.