Why does schlafly believe that the equal rights amendment will actually harm women?

It would degrade the role of wife and mother--The Equal Rights Amendment would secure women's place in the economy and therefore out of the home. 

Phyllis Schlafly believed the ERA would encourage women to enter the workforce instead of take care of their home and children. That role was the most important for women and they had the natural ability to do that job. The ERA would tear apart families and encourage immoral behavior among women. It would also force women to sign up for the draft which Schlafly and many women believed was an improper place for women.