How can I remove slashes from strings?

You can do a number of things here, but the two approaches I would choose from are:

Use str_replace():

$string = "people are using Iphone/'s instead of Android phone/'s";
$result = str_replace('/','',$string);
echo $result;
// Output: people are using Iphone's instead of Android phone's

If the slashes are backward slashes (as they probably are), you can use stripslashes():

$string = "people are using Iphone\\'s instead of Android phone\\'s";
$result = stripslashes($string);
echo $result;
// Output: people are using Iphone's instead of Android phone's

backslashes need escaping

$newstr = "<h1>Hello \ fred</h1>";

echo str_replace('\\','',$newstr);

If it is a quoted string. Use stripslashes