Lead Developer
Sounds like the code you added has an error in it – you can remove that code.
You can do this quite easily using the menu. Just add your phone number as a custom link and add the number as the URL like this: tel:123-456-7890
More info here: https://generatepress.com/knowledgebase/using-menus/
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development