I have a string like below:
$arrayString = "[Orange,Apple,Grape]";
I'm not a fan of
str_replace replacing square brackets because they might be replaced in the array string, so let's
trim them instead, and explode the list on the commas. Given your sample above, this will produce an array of strings.
$arrayString = "[Orange,Apple,Grape]"; print_r( explode(",", trim($arrayString, "][")) );
Array (  => Orange  => Apple  => Grape )
Note: If you have escaped commas, then this won't work.