If I fall into the phase-out range for a tax deduction on a Traditional IRA can I contribute to said account up to my tax deduction limits for said accounts then contribute the rest of my $ to a Roth IRA to reach my overall contribution limit for IRAs in general?
Yes. Without going into the exact numbers, the Roth cutoff is well above the Traditional IRA cutoff, so those right in the Traditional Phaseout range can put the otherwise non-deductible amount into a Roth. You can have deposits to both flavors of IRA so long as the total isn't over $5000 or $6000 if 50 or older.
Per the IRS you are able to contribute up to the limit on a traditional IRA no matter what your income, but if you earn too much the amount which is tax-deductible may go down. There is a limit on Roth IRA contributions if your income exceeds a certain amount.
If you are under 50 years of age at the end of 2011: The maximum contribution that can be made to a traditional or Roth IRA is the smaller of $5,000 or the amount of your taxable compensation for 2011. This limit can be split between a traditional IRA and a Roth IRA but the combined limit is $5,000. The maximum deductible contribution to a traditional IRA and the maximum contribution to a Roth IRA may be reduced depending on your modified adjusted gross income.
Read more at the IRS page.
To answer your question, it depends. I haven't done the math, but the IRS publication provides a form which lets you enter your AGI, the amount deducted for your traditional IRA contribution, and tells you how much you are allowed to contribute to your Roth IRA.
Contributions to either type of account (traditional or Roth) are combined when figuring the limits and what you are allowed to contribute.
Being covered by a retirement plan at work has a significant effect on what you can contribute to an traditional IRA, depending on your income level.
See This Page at the IRS website
I would surely seek confirmation or clarification from a tax expert (I'm NOT one) but the way I am reading what they have, there can be a situation where the presence of an employer sponsored plan and qualifying income levels could prevent you from being able to deduct any traditional IRA contributions from your AGI, but you would still be able to contribute to a Roth if your income was below the cutoff point for Roth contributions.
For something like this I would highly recommend consulting with a CPA or the IRS directly, since there are a lot of variables that affect what you are allowed to do when contributing to an employer provided plan and IRA's at the same time, especially if your income is near the phaseout ranges