Adding phone number links in pdf

If you create the hyperlink in InDesign using an invisible rectangle over the phone number and use the format of tel:1234567890 it will work as long as you export the file as an Adobe PDF (Print). The hyperlink panel will, however, usually show a red dot next to the hyperlink which should only be looked at, in this case, as a caution. When you open the pdf in Acrobat the hyperlink should work to make the phone call. You can double-check that all is well in Acrobat by using the Edit PDF>Link>Edit>Add/Edit Web or Document Link. Double-click on the hyperlink in quwestion and then click on the Actions tab in the Link Properties dialog that appears. If it looks as shown below then all should be well. Sometimes, however,  the computer that you're opening the pdf on's phone system might not be able to make the connection. If that happens attach the pdf to an email to yourself and open the pdf on your cellphone and then press on the phone link. I have found that the connection will always work when I test it this way.

href=tel:1234567890

But I think that will not work in a PDF. It might work unevenly.

https://blog.adobe.com/en/publish/2015/01/07/dial-a-phone-from-a-pdf-link-on-mobile-devices