Richard,
CodeMix will not work with Eclipse 2021-12, so if this is the version you’re using, unfortunately we have no workaround to suggest, other than using a prior Eclipse version.
Like Eclipse, MyEclipse will allow you to install a number of plugins, so you can certainly do PHP development in it after installing the PHP Development tools: https://www.eclipse.org/pdt/ We also have good Javascript support which is constantly updated with MyEclipse releases. Do give MyEclipse a try and let us know if you have further questions.