Can we use PHP in Android Application..is it possible to develop complete Android App with PHP ?

PHP is a server side scripting language. Php is for fetching data from the datastore, perform bussiness logics, then dump the necessary html pages on the browser for rendering. Php does not have ui toolkits. It relies on html. There are html5 and js frameworks like cordova, angular, react etc you can use for that.

The PHP interpreter isn't available on a mobile device, which is why cannot package PHP files into a Android app and expect it to work.

You could however write your backend in PHP and use XMLHTTP calls (in JavaScript) to retrieve data and present it to the user.

One more thing There's no webviev anymore in Android 8.1 new version release that they deleted it . Without Webview we can make progressive web apps and we can still use string in which you will enter iframe . You can make iframe be responsive to all devices and you kinda have your android app.

To develop Android Mobile App through PHP most time three layers required:

1. Android App Layer - where developer has to develop App which will run on Android platform.
2. Web Services - this is back-end service layer, It can be develop in PHP, Java, .NET etc. PHP is most freeware language, and the cost of development also less than others.
3. Database : Last layer where data is saved. Mobile Android App interact with Web services and Web services interact with Database.