Railsでfields_forを使って複数の写真を投稿したい

今某フリマアプリのクローンサイトを作っているのですが写真を複数枚投稿したいのですがうまくデータベースに保存することができません。
今の状態をとしてはProductが親モデルでproduct_image子モデルです。

[1] pry(#<ProductsController>)> params
=> <ActionController::Parameters {"utf8"=>"✓", "authenticity_token"=>"kyCkQIQm9Ze+EUoDs9+vU3n+ceZ4iB+zwZ8K3leUmv7YmfGN5pAVMHp0XuWBNBnLfZTP1Y5VLxVFaYvMW4Rc5Q==", "product"=><ActionController::Parameters {"product_images_attributes"=>{"0"=>{"image"=>[#<ActionDispatch::Http::UploadedFile:0x00007fc7698d9f68 @tempfile=#<Tempfile:/var/folders/5k/4m94gmtd0s153tdmqgr9gmth0000gn/T/RackMultipart20190303-4946-1cn6u8u.png>, @original_filename="phone.png", @content_type="image/png", @headers="Content-Disposition: form-data; name=\"product[product_images_attributes][0][image][]\"; filename=\"phone.png\"\r\nContent-Type: image/png\r\n">, #<ActionDispatch::Http::UploadedFile:0x00007fc7698d9f18 @tempfile=#<Tempfile:/var/folders/5k/4m94gmtd0s153tdmqgr9gmth0000gn/T/RackMultipart20190303-4946-w3y2jr.png>, @original_filename="phone.png", @content_type="image/png", @headers="Content-Disposition: form-data; name=\"product[product_images_attributes][0][image][]\"; filename=\"phone.png\"\r\nContent-Type: image/png\r\n">, #<ActionDispatch::Http::UploadedFile:0x00007fc7698d9ec8 @tempfile=#<Tempfile:/var/folders/5k/4m94gmtd0s153tdmqgr9gmth0000gn/T/RackMultipart20190303-4946-77rqyp.jpg>, @original_filename="phone.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"product[product_images_attributes][0][image][]\"; filename=\"phone.jpg\"\r\nContent-Type: image/jpeg\r\n">]}}, "name"=>"sasa", "description"=>"sasa", "category_id"=>"107", "size"=>"M", "brand"=>"", "product_status"=>"未使用に近い", "delivery_fee"=>"着払い", "local"=>"岩手", "lead_time"=>"2~3日で発送", "price"=>"300", "transaction_status"=>"出品中"} permitted: false>, "controller"=>"products", "action"=>"create"} permitted: false>
[2] pry(#<ProductsController>)> product
=> #<Product:0x00007fc76989a340
 id: 49,
 name: "sasa",
 description: "sasa",
 price: 300,
 likes_count: nil,
 size: "M",
 product_status: "未使用に近い",
 transaction_status: "出品中",
 delivery_fee: "着払い",
 local: "岩手",
 lead_time: "2~3日で発送",
 brand: nil,
 category_id: 107,
 created_at: Sun, 03 Mar 2019 13:32:32 UTC +00:00,
 updated_at: Sun, 03 Mar 2019 13:32:32 UTC +00:00>
[3] pry(#<ProductsController>)> product.product_images
  ProductImage Load (0.3ms)  SELECT `product_images`.* FROM `product_images` WHERE `product_images`.`product_id` = 49
=> [#<ProductImage:0x00007fc76229fd48
  id: 10,
  image: "[\"phone.png\", \"phone.png\", \"phone.jpg\"]",
  product_id: 49,
  created_at: Sun, 03 Mar 2019 13:32:32 UTC +00:00,
  updated_at: Sun, 03 Mar 2019 13:32:32 UTC +00:00>]
[4] pry(#<ProductsController>)>

パラメータはこんな感じです。

product_controller

class ProductsController < ApplicationController

  def new
    @product = Product.new
    @product.product_images.build
    render layout: 'sell-form'
  end

  def middlecategory
    @middlecategory = Category.find(params[:category_id]).children
    respond_to do |form|
      # form.html{redirect_to new_product_path}
      form.json{@middlecategory}
    end
  end

  def smallcategory
  end

  def create
    product = Product.create(product_parameter)
    binding.pry
    redirect_to root_path
  end

  private
  def product_parameter
    params.require(:product).permit(:name, :description, :category_id, :size, :product_status, :delivery_fee, :local, :lead_time, :price, :transaction_status, product_images_attributes: {image: []})
  end
end

渡ってくるproduct_imageのimageをそれぞれちがうインスタンスとして保存したいのですが同じインスタンスの中に保存されてしまっているようです。
解決方法を教えてくださると嬉しいです。