what is purpose of a pin hole sized hole in every phone

[AC Question]

i have observing from several days that my phone has small hole at the bottom and i have checked it for all the phones i dont know the purpose of hole in every phone i wanted to know the use of it please give me answer

 

[Guytronic]

That hole is for the microphone that's used for calls and other voice input such as apps that record sounds.