When you speak on your phone your voice is picked up by your phones microphone your microphone turns your voice into a digital signal with the help of a MEMS sensor and IC
the digital signal contains your voice in the form of zeros and one,
an antenna inside the phone receives this zeros and ones and transmit them in the form of electromagnetic waves, electromagnetic waves transmitted the zeros and ones by altering the waves characteristics such as the amplitude frequency phase or combinations of these. for example, in the case of frequency zeros and one are transmitted by using low and high frequencies respectively. so if one could find a way of transmitting these electromagnetic waves to another phone a call could be established.

to know more go to the link below
https://www.educationpivot.com/post/how-your-mobile-phone-works