It is very simple. You can find word count option in Microsoft word of your Android phone. What you will have to do is
Just open any word document in Microsoft word in which you want to count words. Now go to the main menu option by clicking up and down arrow button. You will see six options I.e. Home, Insert, Draw, Layout, Review and View Options. Now you will have to click on the review option and you will see "word Count" option. Click on it and you will all details of the documents like No. Of pages, word count, character counts etc.
There is another method, you can see the word count in MS Word document by clicking on the down arrow button on onscreen keyboard present at the right-hand side at the lower end. Then you will see a bulb. Click on this bulb and you will find "Tell me what you want". Now type word count in this box and you will find the complete details of the document including word count.
Further, you can also check word count in online websites like " WordCounter.net", "easywordcount.com", "wordcounter.io", "keywordtool.io" and "m.countofwords.com" etc.
For using these sites, you need not install any app for word counting on your phone. Just copy the text you want to count the words and paste in any of the mobile sites and you will find the total word count.
There are several mobile apps are also available at Google play store for this purpose like word counter, novel word counter, text counter, character & word counter, word count camera, word count tool and so on. You can download any of the apps from google play store free of cost and install in your mobile phone and then you can copy and paste the text in the app or just write directly in the app and you will find the total word count.
I hope this will help you.