Of course in many circumstances it is easier to use your phone with your hands. Siri is not meant to replace that. Siri is also not a Voice Control feature. The iPhone has had that for many years now.
Siri is a AI that is used as a digital personal assistant using NLP.
From wikippedia :
"With Siri, Apple is using the results of more than four years of research funded by DARPA via SRI International's Artificial Intelligence Center through the Personalized Assistant that Learns Program and Cognitive Agent that Learns and Organizes Program CALO.
This includes the combined work from research teams from Carnegie Mellon University, the University of Massachusetts, the University of Rochester, the Institute for Human and Machine Cognition, Oregon State University, the University of Southern California, and Stanford University. This technology has come a long way with dialog and natural language understanding, machine learning, evidential and probabilistic reasoning, ontology and knowledge representation, planning, reasoning and service delegation."