The version presented in the exercise, upgraded, looks like this:

View phone number for family member: <$list filter={{!!family}}><$radio tiddler=<<qualify "$:/temp/FamilyContact">> value=<<currentTiddler>>>&nbsp;<<currentTiddler>></$radio>&ensp;</$list>

<$let stateTiddlerName=<<qualify "$:/temp/FamilyContact">>>
  <$transclude tiddler={{{ [<stateTiddlerName>get[text]] }}} field="phone"/>
</$let>

Note that some gymnastics are required with the $set widget and the filtered transclusion passed to the $transclude widget. You might have been tempted to try simply:

<$transclude tiddler=<<qualify "$:/temp/FamilyContact">> field="phone"/>

…but this does not work, for the same reason we had to use a {{transcluded tiddler name}} as the value of the tiddler attribute rather than a "quoted tiddler name" – we want to transclude the tiddler named within the target of the qualify macro, not the tiddler that is the target of the qualify macro.