Creating a reminder with Siri always puts it in "Local" Reminders list

I often use Siri to create a reminder by saying something like Remind me tomorrow at 10 am to xxxxxx where "xxxx" is some activity. Even though I have iCloud for Reminders turned on, those reminders always go into the local Reminders list on my phone. How can I get these Siri-created reminders to go into the iCloud Reminders list?