formulario.php

<form action="" method="post">
    <?php
    $cantidadProductos = 5;
    ?>
    <?php for ($i = 0; $i < 5; $i++) { ?>
        <p>Producto <?php echo $i + 1 ?></p>
        <label for="">Nombre: </label>
        <input type="text" name="nombres[]" required>
        <label for="">Marca:</label>
        <select name="marcas[]" required>
            <option selected value="Marca 1">Marca 1</option>
            <option value="Marca 2">Marca 2</option>
            <option value="Marca 3">Marca 3</option>
        </select>
        <label for="">Precio:</label>
        <input type="number" name="precios[]" required>
        <br>
    <?php } ?>
    <br>
    <input type="submit">
    <input type="reset">
</form>