Can I group in three levels?

I have problems to generate the desired output of an XML using XSL. I want 
to group in three levels

This is the XML to transform:

<?xml version="1.0" encoding="UTF-8"?>
<ROWSET>
  <ROW>
     <ID>27835</ID>
     <NUMBER>29715</NUMBER>
     <PHONE>09876</PHONE>
     <ACT>ACT34</ACT>
  </ROW>
  <ROW>
     <ID>27835</ID>
     <NUMBER>29716</NUMBER>
     <PHONE>62784</PHONE>
     <ACT>ACT87</ACT>
  </ROW>
  <ROW>
     <ID>27835</ID>
     <NUMBER>29716</NUMBER>
     <PHONE>3333333</PHONE>
     <ACT>ACT23</ACT>
  </ROW>
  <ROW>
     <ID>27835</ID>
     <NUMBER>29716</NUMBER>
     <PHONE>3333333</PHONE>
     <ACT>ACT111</ACT>
  </ROW>
</ROWSET>



First I want to group in a first level with the same ID,NUMBER. Inside of 
this first group, a second group with a second
group with PHONE. And finally a third group, inside the second group with 
ACT. I'm not sure if I'm explainig clear.

This is my XSL, that doesn't work

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; 
version="1.0" xmlns:xalan="http://xml.apache.org/xslt";>
<xsl:key name="level1" match="ROW" use="concat(ID,' ',NUMBER)" />
<xsl:template match="ROWSET">
        <ROOT>
     <xsl:for-each select="ROW[count(. | key('level1', concat(ID,' 
',NUMBER))[1]) = 1]">
        <xsl:sort select="ID" />
        <ID><xsl:value-of select="ID" /></ID>
        <NUM><xsl:value-of select="NUMBER" /></NUM>
        <xsl:for-each select="key('level1', concat(ID,' ',NUMBER))">
           <xsl:sort select="PHONE" />
           <PHONE_DATA>
                <PHONE><xsl:value-of select="PHONE" /></PHONE>
                <ACT_DATA>
                                        ????????
                </ACT_DATA>
           </PHONE_DATA>
        </xsl:for-each>
     </xsl:for-each>
     </ROOT>
  </xsl:template>
</xsl:stylesheet>

My desired output for the first XML is:


 <?xml version="1.0" encoding="UTF-16" ?>
 <ROOT xmlns:xalan="http://xml.apache.org/xslt";>
          <ID>27835</ID>
          <NUM>29715</NUM>
          <PHONE_DATA>
                <PHONE>09876</PHONE>
                <ACT_DATA>
                        <ACT>ACT34</ACT>
                </ACT_DATA>
          </PHONE_DATA>
          <ID>27835</ID>
          <NUM>29716</NUM>
          <PHONE_DATA>
                <PHONE>3333333</PHONE>
                <ACT_DATA>
                        <ACT>ACT23</ACT>
                </ACT_DATA>
                <ACT_DATA>
                        <ACT>ACT111</ACT>
                </ACT_DATA>
          </PHONE_DATA>
          <PHONE_DATA>
          <PHONE>62784</PHONE>
                        <ACT_DATA>ACT87</ACT_DATA>
           </PHONE_DATA>
 </ROOT>

 How could I do this?




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