<?php
$filename = "a.txt";
$example = file($filename, FILE_IGNORE_NEW_LINES);
$words = "Emma Jefferson";
$matches = array();
foreach($example as $k => $v) {
    $fullStr = implode(' ', $words);
    if(preg_match("/\b$fullStr\b/i", $v))
        $matches[0][] = $v;
    $str = "";
    $i = 1;
    foreach($words as $word) {
        if ($str === "")
            $str = $word;
        else
            $str .= '|' . $word;
        if(preg_match("/\b$str\b/i", $v))
            $matches[$i][] = $v;
        $i++;
    }
}
$result = array();
foreach($matches as $firstKey => $arr) {
    foreach($arr as $secondKey => $v) {
        $result[] = $v;
    }
}
$result = array_unique($result);
foreach($result as $k => $v)
    echo $v . "<br>";