Please note for step 2 in your set up instructions (wrapping the phone numbers with your class name) you will need to do this directly in the CMS or FTP of the website, unfortunately this cannot be done via GTM.
In your tag manager account, select “Add New Tag”
You then want to select to ‘choose a tag type’ and then from the drop down list select ‘Custom HTML’
Ensure you set the Tag Firing options to once per page. This will ensure Ruler captures data across your whole website.
Then under ‘Triggering’ select ‘All Pages’ from the available list.
Once you have saved the Tag, Push the changes live on to your site.
If you require any assistance with implementation via Google Tag Manager, please let us know.