Switch control

Your iphone could be frozen, so, as already suggested, perform a forced restart of your device.

About switch control, click here:--> Use Switch Control to navigate your iPhone, iPad, or iPod touch - Apple Support

Regards

Giulio

You needed to triple-click the Side button (as written in the warning message you got).

Try to "Force" restart your iPhone:--> Force restart iPhone – Apple Support

Then disable any Switch Control in Settings>Accessibility (or use them being aware of what they do when enabled).

Regards

Giulio