Your code doesnt make sense as you are replacing the whole $row array(meaning you wipe First_Name,Email_Address and everything else in it). If you want to change particular key, use something like:
$row['Phone_Num'] = 'Hidden';
$row['Hide_Num'] = 'checked';
Your code could be exiting because when you initilaized the $row array again, for example $row['First_Name'] would not exist anymore and PHP would give notice for non-existing key.