Check if a string is a pangram or not #exercism

pangram.php

<?php
	function isPangram($param) {
		
		$sentences = strtolower(trim($param));
		$letters = str_split("thequickbrownfoxjumpsoverthelazydog");
		foreach ($letters as $letter) {
			if (!strstr($sentences, $letter))
				return false;
		}
		return true;
	}