When I enter the mobile number using Send Keys the NEXT button suppose to get enable but in this case it stays disabled although then mobile number length is matching = 10.
You should be able to replicate what you do as if you were doing it manually, so what are you not doing?
I can only suggest:
import org.openqa.selenium.Keys as Keys
Mobile.sendKeys(findTestObject('...EditText'), Keys.chord(Keys.TAB))
or
Mobile.sendKeys(findTestObject('...EditText'), Keys.chord(Keys.ENTER))