The phone number exchange may be slightly visible. Here is one way to make the replacement of the telephone number with Search & Replace “invisible.”

With CSS, it is possible to hide the search string and only then display the Call Tracking number after it has overlaid the search string.

See here for detailed instructions:

Artikel on CSS-Selectors

What can I do if script or ad blockers are being used?

There are cases in which the search string cannot be replaced by a call tracking phone number. Script and ad blockers sometimes prevent scripts from running on websites. Individual browsers now also have optional settings that protect against the perceived security risk in a similar way.

In this case, the transparent search string will remain transparent and website visitors will see no telephone number.

Solution

Using the tag <noscript> means that the search string can be displayed if scripts are blocked. The search string will also be displayed in this case.