Ouch, why not just
if(strpos('Los Angeles',$string)!==false)
{...}
But it sounds like these are coming from a SELECT entity in an HTML form, yes?
Are you being nice and putting quotes around all your attributes like a good HTML coder should?
<select name="city">
<option value="New York">New York</option>
<option value="San Francisco">San Francicsco</option>
<option value="Los Angeles">Los Angeles</option>
<option value="Milwaukee">Milwaukee</option>
</select>