Php – How to find a string in an array in PHP

I have an array:

$array = array("apple", "banana", "cap", "dog", etc..) up to 80 values.

and a string variable:

$str = "abc";

If I want to check whether this string ($str) exists in the array or not, I use the preg_match function, which is like this:

$isExists = preg_match("/$str/", $array);

if ($isExists) {
    echo "It exists";
} else {
    echo "It does not exist";
}

Is it the correct way? If the array grows bigger, will it be very slow? Is there any other method? I am trying to scaling down my database traffic.

And if I have two or more strings to compare, how can I do that?