Why is it not possible to take and make calls in FB Messenger on my Lumia?

[Windows Central Question]

IT is just sooo frustrating - I can 'receive' calls on my Lumia WP, meaning I can see them, but I cannot actually take the call. There is no green and red phone buttons to do so. WHY???????? I actually rely on Messenger to communicate with my family members overseas, so therefore I still have to use my trusted old Samsung :-(.