Nothing I've read about the Debut III mentions a built-in phono stage, including Pro-Ject's website, and I've never seen one with an included phono stage either. The current Debut Carbon Phono USB has a built-in phono stage, and maybe an older USB model did, too, but if you have the standard Debut III you'll need your Pre/Pro's phono stage.
If you're worried and want to double check, plug the TT into "tape" and spin a record. What you hear is likely to be very quiet and shelved down in the bass and up in the treble (as all records sound w/o RIAA equalization from a phono pre). If the TT sounds great through the "tape" input, you'll know it does have a phono pre of its own. Trying this won't damage anything. My guess is that you'll end up needing and using the phono stage in your Bob Carver.
Enjoy the TT!
If you're worried and want to double check, plug the TT into "tape" and spin a record. What you hear is likely to be very quiet and shelved down in the bass and up in the treble (as all records sound w/o RIAA equalization from a phono pre). If the TT sounds great through the "tape" input, you'll know it does have a phono pre of its own. Trying this won't damage anything. My guess is that you'll end up needing and using the phono stage in your Bob Carver.
Enjoy the TT!