Previously, Facebook allowed new users to apply it to chat and instant messaging (Facebook Messenger) using it only from the phone number. But Facebook no longer seems to want to continue this policy.

Since 2015, it has not been necessary for Facebook Messenger users to have an account on Facebook, but to use the phone number to call this app. But Facebook has changed its policy recently.

Facebook Messenger users must be registered primarily in Facebook's social media application, a
 new update that passed without being officially disclosed by Facebook but confirmed to the media.