Following along.
Here's the code I have which works for changing the icon but I'm having the same issues about Squarespace now adding http:// to the tel: link.
Change the number in "nth-of-type(3)" to the number of the item (first, second etc)
You can also change the background image to "https://static1.squarespace.com/static/6347793bddaee1636193cb71/t/6369ad0daffa6b66beb0a4ee/1667869965881/Asset+1.png" if you want it to be black.
Any help with the tel: issue would be greatly appreciated!