When you are using this: ${pageProperties.phonenumber}
It will help you to get the data or value on the page. But when it comes to the value present in the dialog, you have to write some Custom JS
Logic in JS,
For current RTE, get the jcr:content node of page, read the value and put that value as the value of RTE field.
Let me know if my understanding is wrong on the question.
Thanks