Is it possible to install Android app in Ubuntu phone? I was searching to have a convenient way of installing Android apps (APK file) in Ubuntu phone.

Can anyone help?
You can't. In fact, Canonical has made a deliberate decision to NOT support an Android runtime in Ubuntu Phone. 

However, now that Android apps are turned into native apps at install time (i.e., ART vs. DVM), it's not unthinkable that a third party could add support for this to Ubuntu Phone. I suggest you check out this thread at the Ask Ubuntu Stack Exchange site.