(PHP 8 >= 8.1.0)
ReflectionEnum::isBacked — Determines if an Enum is a Backed Enum
A Backed Enum is one that has a native backing scalar equivalent, either a string or an int. Not all Enums are backed.
This function has no parameters.
Example #1 ReflectionEnum::isBacked() example
<?php
enum Suit
{
    case Hearts;
    case Diamonds;
    case Clubs;
    case Spades;
}
enum BackedSuit: string
{
    case Hearts = 'H';
    case Diamonds = 'D';
    case Clubs = 'C';
    case Spades = 'S';
}
var_dump((new ReflectionEnum(Suit::class))->isBacked());
var_dump((new ReflectionEnum(BackedSuit::class))->isBacked());
?>The above example will output:
bool(false) bool(true)
