what i've seen about a phantom pg leads me to think that it isn't what you had.
it is possible you had a "chemical pg" or a "blighted ovum" or even a "missed miscarriage." phantom pgs tend to be all kinds of symptoms EXCEPT a positive test result. you had a positive test. that says you were actually pg. simple bloodtests don't always tell the whole story, and i'm a bit surprised that your doctor hasn't already done an ultrasound.
a blighted ovum (you can look it up online) doesn't ever produce a viable embryo or fetus and can stick around for several months before your body finally miscarries. it isn't the baby that produces HCG or progesterone, it is the sac and/or the placenta. you can either wait it out or have a d&c.
a missed miscarriage is best described as an incomplete miscarriage where enough of the placenta and sac are left behind to make your body think you are still pg, but you aren't. that is usually remedied by a d&c.
i agree, you should ask for an ultrasound. progesterone won't bring on your period, only delay it longer. until the placenta and sac are removed your body won't get the hint that there isn't a pregnancy in progress. look up the other possibilities online then go back and talk to your doctor.
hope this helps. it wasn't all in your mind! and it is inaccurate for your doctor to call it a phantom pg, when it wasn't.