Thanks for coming back to me. Sorry the link to view the website currently doesn't work – my client has activated the 'Coming Soon' page.
Is there anyway to add it as a function, as the code you have suggested would be confusing to my client.
I have created the email, telephone and URL custom fields to the 'Directory' custom post type, so it's easy for my client to create directory listings on their website, like in this screenshot:
They just need to add the email, phone or URL to the field and that would automatically become a clickable link in the front-end, if that is possible.