Either-or fallacy. Keeping foreign born Phds out doesn't help us, and doesn't help create more native American Phds. We could strengthen our education system and education culture without Affirmative Action for White Males By Banning Foreigners.
You know, Clinton and Sanders supported policies that would have helped, by dramatically reducing the cost of college. Upper level advanced degrees are a filter/pipeline issue, and the more people in 2-year and 4-year programs, the greater number who might advance to graduate level.
The reason there are so many foreign Phds is that they often completed (free) 4-year programs in their home country, and go abroad for graduate degrees. My wife completed her masters degree in China, then came here and got a second masters degree.
What I hear you saying is "if only we banned these foreigners, maybe our native born people would have a chance in Phd programs". And what I interpret that to mean is "Let's not spend $80 billion on free college for everyone who wants it, because that would be 'big gubmint socialism', instead everything will work out if we just institute protectionism immigration policies."
I say, let's continue to drain the smartest people in the world to our shores and educate our own as well.