How to implement audio calls in the application?

Question

Mobile development

I apologize in advance for a possibly stupid question, I just haven’t come across it yet and haven’t found any information.
It is necessary to develop a small messenger, a local analogue of telegram. I will be developing api in PHP and another front developer.
I stumped the question of the implementation of audio and video calls.
Is this generally a server task with an api or a front? And if the server, then by what means to implement it, I will be glad of any help. Please do not ask questions like "What does telegram not like?".

Answer 1

Through api Quickblox'a, for example.