$re = '/agent-\d+-\d+:([a-zA-Z0-9!@#$&?()-.+,\/\'<>_]*\s+)*(?<!(my phone number)\s*([a-zA-Z0-9!@#$&?()-.+,\/\'<>_]*\s+){0,15}\S*)<PHONE_NUMBER>/m';
$str = 'you\'re very welcome. my phone number is on your caller id as well, <PHONE_NUMBER>.. agent-480000-486000:<PHONE_NUMBER> um, did you';
preg_match_all($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