1
resposta

Ao utilizar o namespace a classe deixa de ser encontrada.

<?php

namespace Modelo;

use modelo\cpf;
Class CPF {
private   $cpf;
 public function  __construct ( string $cpf) {    
    $this -> cpf = $cpf;
   }
public function recuperaCPF() : string {
    return $this-> cpf;
} 

}

Ao rodar

Interactive shell

php > require 'C:\Users\rlirio\Documents\ProjetoPHP\Modelo\cpf.php';
php > $cpf = New CPF('1212131414');
PHP Warning:  Uncaught Error: Class 'CPF' not found in php shell code:1
Stack trace:
#0 {main}
  thrown in php shell code on line 1

Warning: Uncaught Error: Class 'CPF' not found in php shell code:1
Stack trace:
#0 {main}
  thrown in php shell code on line 1
php >                                                                                            
1 resposta

Já tentou usar um require para chamar a classe?