Update to-be-recorded phrase_en.xml

docs/phrase/phrase_en.xml

@@ -491,6 +491,7 @@
 	  <prompt phrase="Normal clearing" filename="ivr-normal_clearing.wav"/>
 
       <!-- The following phrases still need to be recorded -->
+      <prompt phrase="This conference is full. Please contact the conference moderator." filename="conf-conference_is_full.wav"/>
     </ivr>
 
     <misc>