To elaborate on the comment made, with the information available that you want to share, your code works as advertised, regardless of whether magic_quotes_gpc is set or not. It will not attempt to perform any arithmetic on the strings, and magic_quotes_gpc will not affect the way simplexml parses it's data.
~/temp ► cat foo.xml
<example>
<node-ex>
<identifier-1>ValueOfIdentifier1</identifier-1>
<phone-number-1>141 555 1414</phone-number-1>
</node-ex>
</example>
~/temp ► cat test.php
<?php
$root = simplexml_load_file("foo.xml");
echo $root->{'node-ex'}->{'identifier-1'} . "\n";
echo $root->{'node-ex'}->{'phone-number-1'} . "\n";
~/temp ► php test.php
ValueOfIdentifier1
141 555 1414
~/temp ► php -dmagic_quotes_gpc=1 test.php
ValueOfIdentifier1
141 555 1414
Of course, if your example isn't the same as the data you're actually using, that might be the issue. If magic_quotes_gpc is enabled, using stripslashes() should reverse it, and then it should work. If you're not using a constant string, but a variable -- that might be the cause of the issue. There is however nothing in your example that indicates anything that should be affected by either magic_quotes_gpc or using "-" in the property name.