docker-compose picks wrong version of php

I've got trouble using docker-compose. docker-compose picks wrong version of php.

networks:
  laravel:

services:
  nginx:
    image: nginx:stable-alpine
    container_name: nginx
    ports:
      - "8088:80"
    volumes:
      - ./src:/var/www/html
      - ./nginx/default.conf:/etc/nginx/conf.d/default.conf
    depends_on:
      - php
      - mysql
    networks:
      - laravel

  mysql:
    image: mysql:5.7.22
    container_name: mysql
    restart: unless-stopped
    tty: true
    ports:
      - "4306:3306"
    volumes:
      - ./mysql:/var/lib/mysql
    environment:
      MYSQL_DATABASE: wrong
      MYSQL_USER: wrong
      MYSQL_PASSWORD: secret
      MYSQL_ROOT_PASSWORD: secret
      SERVICE_TAGS: dev
      SERVICE_NAME: mysql
    networks:
      - laravel

  php:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: php
    volumes:
      - ./src:/var/www/html
    ports:
      - "9000:9000"
    networks:
      - laravel

  composer:
    image: composer:1.10.22
    container_name: composer
    volumes:
      - ./src:/var/www/html
    working_dir: /var/www/html
    networks:
      - laravel

docker file is

FROM php:7.3-fpm-alpine

RUN docker-php-ext-install pdo pdo_mysql  

and I run these commands

docker-compose up -d --build

docker-compose run --rm composer install

and I got this message

This package requires php ^7.1.3 but your PHP version (8.0.6) does not satisfy that requirement.

I put down php7.3 in dockerfile, but php(8.0.6) installed. I don't know why.

I tried docker system prune -a, and run the commands, but still doesn't work.