Android is the OS for android phones/tablets and its based on java. PHP is a programming language for developing websites.
So Android is only good if you want to develop for Android mobile devices and nothing else.
PHP lets you work as a web developer so the scope is much larger.
Of course, the real question is why pick one? Most developers know several languages after they've been working or studying for a while. I would suggest starting out with PHP as it is pretty easy to start with and picking up Android later, or java or .net or ruby...
Hey ANdroid is current trends and PHP is along so ANdroid would be hot for you to pic.
Let me tell you you go with the interest and the previous learning record of yours. For android you need the Java while PHP is stand alone. If you have felequnce in java go for android while if php is better go for PHP rather thinking that Android is hot so i must chooose it.