Siri can be summoned hand-free if you have the “Hey Siri” feature turned on. Once you do that, all you have to do is say “Hey Siri” and then give your command. To turn it on, go to Settings/Siri & Search.
If that switch is not on, turn it on. You may be asked to train Siri to listen for your voice. If so, just do what it says on the screen. It takes only a minute to do it. From then on, your iPhone (or iPad) will listen for the keywords “Hey Siri” and then do whatever else you tell it to do.
“Hey Siri” doesn’t work for every iPhone nor every iPad. It works on newer ones. It doesn’t work on older ones. It works on in-between ones but only when they are charging. The reason for this: “Hey Siri” uses a little bit of battery power, because it’s listening. Newer iPhones and iPads have special low-power chips made especially for this sort of task, so they don’t have to be charging for Hey Siri to work. Learn more about which devices work with Hey Siri at Apple’s site.