How Can Tell If Its A Real Pregnancy Or A Phantom Pregnancy In A Dog?

The only way to do that is to have the test(s) done by the vet. It's standard protocol to do the ultrasound or x-rays and extremely important. Any prenancy and whelping and nursing period should be closely monitored by your veterinarian. :-)
The physical signs can be change in appetite (decrease usually earlier and increase later), bigger milk glands, behavioral changes (also sign of uterine infection), and of course a bigger belly (also sign of uterine infection).
HOWEVER that is not accurate and many of the signs can also be signs of a possibly deadly uterine infection. You can't tell usually just by looking or behavior or even because their body changes. Many go through false pregnancy so it is not an accurate way to tell. It is recommended dogs that have repeat false pregnancy be spayed (most dogs really for health and overpopulation issues) because of hormonal issues. My favorite way to tell is the ultrasound. It is easy, non-invasive, and you can tell the earliest this way. And you can get a picture of them before their even born! You can also tell if it's an infection that's present and not pups and catch it sooner than before your dog is critically ill. 20 to 30 days in your vet can feel for particular lumps that let them know she's probably pregnant, after that they can't feel them and what they are feeling for kind of blends in to everything else. Mid-way a repro test can be run (ask your vet). And 45 days and after an x-ray can be run and they can have a good idea of how many pups by how many skeletons show up on the x-ray.
The visuals can be invaluable in spotting potential problems before they occur or knowing whether your pup is better off actually whelping under the supervision of your veterinarian because there is likely to be a problem.

Gestation period is usually 59 to 63 days but they can go a little sooner or a little later. 70 and you need to call your vet. Start taking her temperature around day 57 - 59 (or when the colostrum comes in, whichever) if the vet (or you) doesn't think you should sooner. Normal average temp is 101 to 102 but usually closer to 102. When she drops to 98 (or 99) it'll be within the next 24 hours.

It is also very important to know whether your breed is prone to complications during pregnancy and whelp and whether or not your breed is a standard c-section breed and any other particulars about your breed.

www.learntobreed.com
www.dogbreedinfo.com
www.diamondsintheruff.com
www.dogfoodanalysis.com
http://drnelsonsveterinaryblog.com/2009/01/01/canine-labor--when-to-call-the-vet.aspx?ref=rss