input: Write a function to create an application using Python and Flask that allows users to submit form data containing fields for Name, Email, and Phone, and stores this data in a SQLite database. The function should return a Flask app instance that handles the form submissions.
  assert create_flask_app().route['/submit'].methods[0] == 'POST'
  assert create_flask_app().template_folder == 'templates'
  assert 'data.db' in create_flask_app().config['SQLALCHEMY_DATABASE_URI']
output: def create_flask_app():
      from flask import Flask, request, render_template
      from flask_sqlalchemy import SQLAlchemy
  
      app = Flask(__name__, template_folder='templates')
      app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///data.db'
      db = SQLAlchemy(app)
  
      class User(db.Model):
          id = db.Column(db.Integer, primary_key=True)
          name = db.Column(db.String(80), nullable=False)
          email = db.Column(db.String(120), nullable=False)
          phone = db.Column(db.String(20), nullable=False)
  
      @app.route('/submit', methods=['POST'])
      def submit():
          name = request.form['name']
          email = request.form['email']
          phone = request.form['phone']
          new_user = User(name=name, email=email, phone=phone)
          db.session.add(new_user)
          db.session.commit()
          return "Data submitted successfully"
  
      return app