Basic object oriented programming in php

<?php

function is_phone_number($number){
$length = strlen($number);
if($length == 11){

for ($i=0; $i < $length; $i++) { 
if(ord( $number[$i]) < ord('0') ||  ord( $number[$i]) > ord('9')){
return false;
}
}
return true;
}
return false;
} 

class Person {
public $name;
public $profession;
public $phone_number;
public function check_phone_number($phone_number){
if(is_phone_number($phone_number)){
$this->phone_number = $phone_number;
}
}
}

$polo = new Person();
$polo->name = 'Polo dev';
$polo->profession = 'Student';
$polo->check_phone_number('01670978989');

echo $polo->name . '<br>'; 
echo $polo->profession . '<br>'; 
echo $polo->phone_number . '<br>';