Facebook is a largest social media network at the moment. The company has invested in many apps like WhatsApp, Instagram and now the company has made its interest in creating Dialer apps for Android.
Android Police has receive a screenshot which talks about a Facebook app. The feature was not meant to go public as it is presented by tag which says "FB only". It looks like someone launched it by an accident.
According to app's description, the app will act as a Caller ID to identify who is calling you. It also noticeably able to block numbers automatically based on commonly blocked noumbers.
We are not sure about that the Phone app will ever be made a reality as Facebook conducts many experiments with apps and services that might not be bring to the consumers. But we'll keep a lookout for more information regarding this app.