PHP is way too easy to learn and provides too many job opportunities to ditch it completely even though ObjectiveC jobs pay more at the moment. Also there are cases when you can use both languages in client-server applications. I'd suggest to emphasis on iOS / ObjectiveC while creating sites using PHP as hobby.
As more and more people get iPhones and use Apps more often, they search for websites less often. I use the web a LOT less now than I did a year ago... Try iOS...
In my opion PHP developer is the best because PHP is the contraction for Hypertext Preprocessor, which is one of most popular open source programming languages.
PHP is open source. Open source always rocks !!!! Now Android has more apps then iphone as i allows every one to contribute easily With IPhone you have to bear a lot with apple guys when you submit your app on itunes connect for review.
PHP will be over-crowded soon, it most likely already is. Unless you've got a unique set of skills using PHP and can do amazing things with it, I'd say learn a new language and build your collection of languages up, so you've got more than just a PHP skillset.
I'd say that an iPhone developer will make more, at the moment. However, as a developer, you need to stay up to date on a few languages to be marketable. So I'd say both.
As i known for making a dynamic type of website php is very useful in them . PHP is a general-purpose server-side scripting language originally designed for Web development to produce dynamic Web pages.