alex-feng
I can't access backend of your site to update for you so you can try with these steps:
1 - Go to Global Configuration in admin panel > disable 'Default Editor' by set it to 'None'
2 - Go to admin panel > Extensions > Modules > open that custom html module for social > add this line of code:
<li><a href="tel:123456789" title="Call 123456789"><span class="fa fa-phone" aria-hidden="true"></span><span class="element-invisible hidden">empty</span></a></li>
Like this: https://prnt.sc/r3bv7w