Activate Siri and other functions just by nodding your head
Apple has a wide range of specialized features for users with limited mobility that can radically change the queues you use to control your phone. One of the coolest is the Switch Control feature, which transforms your camera into a motion sensor that will activate certain functions -- for example, you can bring up Siri by turning your head to the right.
The set-up is a little involved, but here's how to do it: go to Settings > General > Accessibility > Switch Control. Here, turn on Switch Control, tap Scanning Style, and select Manual. Then, tap Switches > Add New Switch > Camera > either Left or Right Head Movement > and select your desired function (you have your pick from eight functions, including Siri, the App Switcher, and the Home button). Now, any time you turn your head, you'll activate what you picked (and when it inevitably gets annoying, just tap the Switch Control radio button off).