You are using the SDI, as opposed to, the MDI Interface. You cannot use Threads in an SDI Application and the Phone Monitor needs to be started as a Thread.
The Phone Monitor needs to be able to open its own Window (with its own Accept Loop) so that it can operate in the background. In order for this to work in Clarion, your Application needs to use an "Application" Window as its Main Window. Threads in Clarion will only work if your Main Window is an Application Window.
If your program only needs to display a Dialog Box, with no Child Windows, then the Phone Monitor Template will not work, as written. What you can do, however, is copy the Source Code from the Phone Monitor and paste it into your Application. Most of the work is performed in the Timer Event.