The 14th Amendment* as modified by the 19th already does everything the ERA* would have done. It is already illegal and unconstitutional to pay women differently, or use gender as a critera for hiring, or any of the other abuses the ERA is meant to stop. The problem with gender equality in this country is not "there is no law to protect women" (which can be solved by something like the ERA), but a combination of "women aren't being treated equally despite the law" and "women suffer disproportionally from a lack of certain worker's protections for a variety of reasons" (a problem that simply making gender discrimination more illegal won't help).
These are not unsolvable problems, but they need to be addressed by measures that actually target the proper problem. For example, a measure guaranteeing paternity leave would help reduce the pressure on the mother of a new child to take time off (more than is medically necessary), which would in turn reduce the common "less time in position" issue that contributes heavily toward the pay gap.
*
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside. No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
**
"Equality of rights under the law shall not be denied or abridged by the United States or by any State on account of sex."