Using commas in a PHP IF statement value

I have a PHP IF:

<?php if ($variable['model'] == '172 I, K, L, M Skyhawk,172 N Skyhawk,172 P Skyhawk')

The 172 I, K, L, M Skyhawk is ONE value, I am not sure how to make it appear as one value as it seems it is working as 172 I, then, K, then L etc.

Thanks in advance for the help