Removing spaces with preg_replace outputs unrecognized characters in string in php

i want to replace multiple spaces or   with one space so i have tried below code using preg_replace function,

so it replaces spaces correctly but it also puts unrecognized characters in output string,

for demo i am taking $string variable but in actual it can be data from serverside database, see below code:

<?php 
     $string = "123080345&nbsp;900113760  165604100012";
     echo preg_replace("/(\s|&nbsp;)+/",' ',$string);

     //output: 123080345� 900113760� 165604100012
     //expected output: 123080345 900113760 165604100012

So my question is why preg_replace putting unrecognized characters and how to get clean and clear output,

which doesn't have unrecognized characters as i have shown in above code as expected output

Solution

Although it's just string with numbers, spaces and  ,

but i think in database it is UTF-8 encoded string so when i have tried preg_replace it is returning unrecognized characters.

so it's working when i have tried same regular expression with /u identifier for unicode

so below is my solution:

<?php 

     $string = "123080345&nbsp;900113760  165604100012";
     echo preg_replace("/(\s|&nbsp;)+/u",' ',$string); //u for unicode characters 

     //output: 123080345 900113760 165604100012

i hope it can be helpful to someone, thanks.