$re = '/(?:
(\((?>[^()]|(?1))*\)) # Match (..(.)) like substrings
|
({(?>[^{}]|(?2))*}) # Match {{.}..} like substrings
)
(*SKIP)(*F) # Ignore the texts matched
|
(?:FIRSTNAME|LASTNAME|PHONE|EMAIL)/x';
$str = 'FIRSTNAME LASTNAME PHONE EMAIL {FIRSTNAME LASTNAME PHONE EMAIL{FIRSTNAME LASTNAME PHONE EMAIL }FIRSTNAME LASTNAME PHONE EMAIL }';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php