How can i add an icon to button

Hi, guys!
I just installed grav skeleton one-page based on Quark theme. I just need to add an icon to button placed on hero picture.
Button code is
[button_name](../some-page?classes=btn)
How can i add an icon from font awesome or integrated icon font to this button?
If i just correct code to
[<i class="fa fa-phone"></i>button_name](../some-page?classes=btn)
i just see an tag text instead an icon.
Pls help me