Docker PHP Failed to Open Stream: Permission Denied on Image Upload

I'm building a PHP/Docker web application. I have an HTML form where a user can upload an image and it will be stored into a local directory. I am using the W3Schools file upload example.

However, I'm getting a Permission Denied error when trying to upload via the form: Warning: move_uploaded_file(image/listingsorchid.jpg): failed to open stream: Permission denied in /var/www/html/process-listing.php on line 59.

I am using the php-docker-simple_php image. I used docker exec -it 9381479b00e6 sh and whoami to confirm the image is running as root. file_uploads = On is enabled in my local php install.

My Dockerfile looks like this:

FROM php:7.4-apache
RUN docker-php-ext-install mysqli

And my docker-compose looks like this:

version: '3.1'

services:
  php:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - 80:80
    volumes:
      - ./src:/var/www/html/

  db:
    image: mysql
    command: --default-authentication-plugin=mysql_native_password
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - mysql-data:/var/lib/mysql

  adminer:
    image: adminer
    restart: always
    ports:
      - 8080:8080

volumes:
  mysql-data:

A user in this thread suggested creating an uploads.ini that would set file_uploads = On and including that in the Dockerfile. I've created an uploads.ini, but I'm unsure how to implement this into my Dockerfile or if it would work.

What should I do to resolve this error?