You can go to Settings > Sounds & Notifications > Reminder Pop-ups and customize your choices.
For example, if the third option is selected, reminders will not pop up when your phone is in full screen mode.
Customize the setting of a Reminder pop-up
You can go to Settings > Sounds & Notifications > Reminder Pop-ups and customize your choices.
For example, if the third option is selected, reminders will not pop up when your phone is in full screen mode.