替换动态字符串的中间部分

Question

I know this can be done using preg_replace but I have no idea how to set it up and the only examples I can find online all use a pre defined string (ie - $text = 'this is my text';).

I need to replace certain parts of the string which is being called dynamically from the database with the letter 'X'.

For example.

  $from = $row["From"];

Right now, echoing $from will show something like :

 011234567889

I want it to output something like :

 01123XXXX889

I'm really stumped here so any help greatly appreciated.