iPhone showing reminders, but I have none
When you open the Reminders app, make sure there isn't anything set in both Reminders and Tasks.

You may have created a Task using Siri, or another app by accident. And as a result of the way the app is setup on the iPhone, it doesn't default to showing you both Reminders and Tasks at the same time.

On the iPhone try the following:


Open up the Reminders app
Tap near the bottom of the screen (you should see other white tabs)
Tap on whichever tab is not active (most likely Tasks)
If there are any items listed there, check them off by tapping the circles next to the name


On the Mac try the following:


Open up the Reminders app
Ensure sidebar is visible by going to View > Show Sidebar in the top Menu Bar
Click on all of the different options in the sidebar (Today, Reminders, Tasks, etc)
If there are any items listed there, check them off by clicking the circles next to the name