Icons Not Displaying

I’m using your plugin with an emergency locksmith website for a client but the icon has stopped displaying with both of the following codes, which are working fine on other websites I’m using your plugin with:

<i class=”fa fa-phone”></i>
<i class=”icon-phone”></i>

I can see the code above with inspect elements using Chrome.

Any ideas? I’ve disabled all other plugins but it’s still not working. I can confirm it was 100% working only last week and I haven’t made any changes since.

https://wordpress.org/plugins/lead-call-buttons/