gmaillinks
Gmail is smart enough to turn telephone numbers into links (most of the time) and so they make them available to click on:
They are a standard telephone link in the format of:
<a href="tel:323-601-1200">323-601-1200</a>
While browsing the web I have a handler set for the tel: protocol and it works fine, but inside Gmail it wants to use the builtin dialer:
How can I keep Gmail from using the dialer for tel: links in email messages?
If you already have the addresses in a group, two methods come to mind.
If you'd just rather type one email address and have it go to everyone, there are a multitude of services where you can do that. Google Groups is one. (But that's probably overkill for five people.)
Access Gmail, and click an icon of the shape of overlapped double diamonds, next to the star icon in the omni-box where the URL is displayed.
If you don't see it, try reload the page.
Best Answer
Copy from browser
What I do is I generate the HTML to be visible in any website (a blog, one of my sites, a simple html local file written in Notepad, etc.) and then I simply copy the content selecting it directly in the browser and pasting it directly into the signature.
It's been lots of help for decades.
I just recently noted the new version of Gmail destroys those "tel:" links (even though it's a valid current protocol). I've already sent a comment to Google from the last link in the upper-right config menu.
If many people ask for it soon, they will certainly repair that faster.