I have a variable `$mobileno` which contains mobile number and sometimes multiple number separated by /(Forward slash) and I used the following code to replace the slash(/) with comma(,). But my code isn't working.

```
$str = str_replace('9875647362/985634758', ',', $str);
 //mobile numbers are stored in $mobileno
print_r($str);//expected output is 9875647362,985634758

```

Please help me.