While there is no direct integration with Siri in Pocket Lists (but it is scheduled to be added in future releases), using Siri for Pocket Lists is possible in two ways:
- Via the Reminders & the Calendar apps.
- Via Siri Shortcuts.
Reminders & 
Calendar
Pocket Lists provides a realtime data import from Apple's basic Reminders and Calendar apps which can be enabled in the Pocket Lists app's Settings > Import screen.
Pocket Lists updates the import every time you launch the app and every time the iOS throws an event that a new event/task has been added on the Reminders / Calendar side.
This means that you can enable the data import and then use Siri for adding reminders and events to the Reminders / Calendar apps, and this data will be eventually imported into Pocket Lists.
The big benefit of such via-Reminders-and-Calendar-integration is that you don't need to pronounce Siri "In Pocket Lists, do something..." which would normally be required for any third-party app. Instead, you may use basic commands which are exclusive for the Reminders and the Calendar apps — such as "Remind me to", "Add milk to my shopping list", "Add an appointment", etc. — and the result will get into Pocket Lists via the import.
Siri Shortcuts
Pocket Lists supports Siri Shortcuts.
Head on the Pocket Lists' Settings > Siri Shortcuts to see the list of all available shortcuts, and dictate your favorite shortcuts (voice commands) to activate the Pocket Lists functionality:
- Add a to-do
- Add a list
- Show my lists
- Show what's up next (scheduled to-dos)
- Show what's nearby (to-dos assigned to nearby locations)