The organizing body should have seen this coming. A dogmatic adherence to the 'call for paper' rules was an error. They needed to survey the field and if 25% of PHP programmers in the wild are women, they should attract by subsidy or otherwise a comparable - even greater, number of women to address the group.
This sprt of problem is rampant in the hard sciences and the entire ecology is slanted away from higher representation by women at all levels and in all disciplines.
It is all apparently driven by the free will of the women, but I think it runs deeper and is societal - there are comparable enclaves where women are more highly represented than men. A call to Miss Google shows this:- https://www.google.com/search?q=disciplines+dominated+by+women&spell=1&sa=X&ved=0ahUKEwjpse6juaXkAhVOtlkKHanPAokQBQgvKAA&biw=1920&bih=1008
Some say that simply placing women into the mix would solve the problem, but most women have better things to do than stand up in front of a bunch of partly hostile men - I think most men feel the same way, it takes a special breed of person to want to go to meetings and yap at others - who may be heckling or otherwise crotocal
The way to approach it is to approach woman led php or other wider programming groups to assist in levelling the field to whateverr degree would suit the poblem. as time went by, women would feel more welcome at such groups. Any moderator should slap down any asshole who adversely heckled any (male of female) speaker so academic meeting decorum is maintained.