Its a pain in the ass to all the time have insert hard code in the functions.php file to remove required phone on the checkout page. Why is there not a plugin that can do this for us that don’t want to tamper with the code?
Well, there are, at https://kingplugins.com/product/woo-remove-required-phone you can get a plugin that does just that, and nothing more, except giving you the possibility to turn that function on or off by ticking a box.
And why should you not require a phone number from your customers? Because some people just don’t want to give out their number, and you don’t want to lose them for a small issue like that do you?