“We want customers to be able to click on our telephone number on the support web page, and have Microsoft Teams dial the number.”

Three ways to do it, not supported in all browsers unfortunately:

<a href=”tel:555 1212″>555-1212</a> 555-1212

<a href=”callto:555 1212″>555-1212</a>

<a href=”skype:555 1212″>555-1212</a>

tel: has a RFC (proposed) standard explaining it’s use – RFC5341 – IANA Registry for TEL URI Parameters
(by default, tel: is the only one linkable by WordPress)