driver = webdriver.PhantomJS("phantomjs.exe", desired_capabilities = dcap)
webdriver.DesiredCapabilities.PHANTOMJS["phantomjs.page.settings.javascriptEnabled"] = False
webdriver.DesiredCapabilities.PHANTOMJS["phantomjs.takesScreenshot"] = False
webdriver.DesiredCapabilities.PHANTOMJS["phantomjs.page.clearMemoryCash"] = False

browserName:phantomjs
version:2.1.1
driverName:ghostdriver
driverVersion:1.2.0
platform:windows-7-32bit
javascriptEnabled:true   # Should be false
takesScreenshot:true     # Should be false

phantom_exc_uri='/session/$sessionId/phantom/execute'
driver.command_executor._commands['executePhantomScript'] = ('POST', phantom_exc_uri)
initScript="""
this.onInitialized=function() {
    var page=this;
   ### disable javascript and screenshots here ###
}
"""
driver.execute('executePhantomScript',{'script': initScript, 'args': []})