using Rule::exists for a specific ID

Hi all,

I think I'm missing something here, or perhaps I'm not understanding the docs.

I am trying to add a validation rule in a form request to check that the ID I'm posting already exists in my database. So I thought this would work:

    public function rules(): array
    {

        return [
            'telephoneId' => [
                'required',
                Rule::exists('telephones')->where(function (Builder $query): void {
                    $query->where('id', $this->telephoneId);
                }),
            ],
        ];
    }

but I just get the error The selected telephone id is invalid.

So just to test further I did this:

               Rule::exists('telephones')->where(function (Builder $query): void {

                    $t = Telephone::first();
                    $query->where('id', $t->id);
                }),

same error message.

Have I misunderstood how this works?