Why is my withdrawal from my Roth being partially taxed? It has been in the Roth for several years,

Has your Roth been established for 5 years?  Your Roth IRA withdrawals may be taxable if:

• You’ve not met the 5-year rule for opening the Roth and you are under age 59 1/2.  You will pay income taxes and a 10% penalty tax on earnings that you withdraw. The 10% penalty may be waived if you meet one of the exceptions to the early withdrawal penalty tax.
• You’ve not met the 5-year rule but you are over age 59 1/2: Earnings withdrawn will be included as income and subject to income taxes but will not be subject to a 10% penalty tax.
• You’ve met the 5-year rule but are not yet 59 1/2: Earnings withdrawn will be considered as income and subject to income taxes and a 10% penalty tax. The 10% penalty may be waived if you meet one of the exceptions listed on page 64 of IRS Publication 590-B - Distributions from Individual Retirement Arrangements

The last bullet should generally just say "You are not yet 59½."  Meeting the 5-year rule for qualified distributions is irrelevant for anyone under age 59½ unless that person is disabled, deceased, or is using the money for a first-home purchase.