I have had success with this by creating a hyperlink using an invisible rectangle for a hyperlink (rather than the text) and then exporting as an Adobe PDF (Print) rather than an interactive PDF. You'll note that the phone number (including the "long-distance" 1) has no spaces or dashes after the "tel:" prefix or between numbers. You'll also notice that the Hyperlink dot is red in InDesign saying that it is not an active link. That is because the formatting used for the hyperlink is done in the way that Acrobat recognizes a phone link which differs from the way that InDesign does. Once you open the pdf in Acrobat you should be able to click on the phone number and have the call placed. This way has always worked for me.