I think if the phone number is defined within an anchor, the 'smartphone' will recognise this and use the relevant phone application.
See what other websites to that facilitate this.
For Jquerymobile theme in APEX 4.2, this should work:
In Page Item definition you have a section "Settings", here you can set "Subtype". Choose Phone number.
The subtype-option is only available for Text Field items.
I think OP was talking about a link to call an existing number, not entry of a new one.
Then put the field read-only attribute to 'Always'. That way the field will show as a phone number and you use a native APEX solution and don't have to add your own element attributes.
I think the native Apex solution may be a good idea. Thank you.