MaryK4's original reply is entirely incorrect. Code G is the correct code for your in-plan Roth rollover (which is a type of direct rollover).
The amount that the payer reported in box 2a is the taxable amount. Enter the Form 1099-R exactly as received. On the page that follows, indicate that you moved the funds to a Roth 401(k) and TurboTax will include the taxable amount on Form 1040 line 5b with the ROLLOVER notation.
