If you have already disabled the notifications in your phone settings > notifications, then this is how to turn off via your Facebook app.
- Go to your facebook app and to the newsfeed area.
- At the bottom right, click the “more” link
- Scroll down and click on Settings.
- Click notifications
- Click birthdays, then uncheck to turn off.
That is all and good luck.
Dr. Elijah Clark (November 30, 2014). Turn off annoying Facebook birthday notifications on iPhone iOS [Web log post]. Retrieved from https://elijahclark.com/turn-off-annoying-facebook-birthday-notifications-on-iphone-ios/