Is there a FM imbedded link used for phone numbers that in a pdf file activates the number on a smart phone?

What happens when you use Marker Type: [Hypertext]
and a URI of form:

message URL tel:1234567890

In a quick test, this survives to PDF as hypertext, gets handed to my default browser, which (being a desktop machine) throws a dialog saying, in effect "Just what am I supposed to do with this? I'm not a phone you know." My phone, on the other hand has two PDF readers (Kindle and some shovelware office ap), neither of which appear to even notice the URL (which I take to be not FM's fault).

The hand-off to email is not something that FM (or Acrobat) does per se. As far as I know PDF readers merely hand the URI to the host operating system. If the host knows what a "tel:" scheme name is supposed to do, it gets done. For a more or less complete list of scheme names, see the wiki page.

Be sure to use fully qualified international dialing numbers.

And be sure to avoid mistake 0 of FM hypertext markers: in addition to inserting the marker, it has to be within the scope of a unique Character Format applied to the text string to be made active. This tag doesn't even have to apply any visible effects, but it does have to be there, as it's how FM determines the boundaries of the hyper region. A Character Format set to Family:Default ¶ Format (and all else blank or As-Is), named "URI", would suffice.