Why a function checking if a string is empty always returns true?

I have a function isNotEmpty which returns true if the string is not empty and false if the string is empty. I've found out that it is not working if I pass an empty string through it. function isNotEmpty($input) { $strTemp = $input; $strTemp = trim($strTemp); if(strTemp != '') //Also tried this "if(strlen($strTemp) > 0)" { return true; } return false; } The validation of the string using isNotEmpty is done: if(isNotEmpty($userinput['phoneNumber'])) { //validate the phone number } else { echo "Phone number not entered<br/>"; } If the string is empty the else doesn't execute, I don't understand why, can someone please shed some light on this please.