How to change given icons via filter?

Hello,

in this case i would like to change the icon of the phone right before the number. Now I have my own svg-file I would like to put there instead of the font-awesome stuff. I figured out I could use the geodir_custom_field_output_phone_var_{$html_var} filter, but how do I build this function. I got one ready to use function from you guys for removing the address icon. It does it’s job but i still don’t know how this thing works. There is so much code that doesn’t affect the icon itself, so it’s more confusing for me.

I mean there must be a way to change this in like 5 lines of code. Like get this and replace – Boom.

Regards Falk