input: Write a function to create a Flask application that allows users to submit form data including Name, Email, and Phone, and stores this data in an SQLite database. The function should return the Flask app object.
  
  assert create_flask_app() is not None
output: def create_flask_app():
      from flask import Flask, request, render_template_string
      import sqlite3
  
      app = Flask(__name__)
  
      conn = sqlite3.connect('user_data.db')
      cursor = conn.cursor()
      cursor.execute('''
          CREATE TABLE IF NOT EXISTS users (
              id INTEGER PRIMARY KEY AUTOINCREMENT,
              name TEXT NOT NULL,
              email TEXT NOT NULL,
              phone TEXT NOT NULL
          )
      ''')
      conn.commit()
      conn.close()
  
      @app.route('/', methods=['GET', 'POST'])
      def index():
          if request.method == 'POST':
              name = request.form['name']
              email = request.form['email']
              phone = request.form['phone']
  
              conn = sqlite3.connect('user_data.db')
              cursor = conn.cursor()
              cursor.execute('INSERT INTO users (name, email, phone) VALUES (?, ?, ?)', (name, email, phone))
              conn.commit()
              conn.close()
  
          return render_template_string('''
              <form method="post">
                  Name: <input type="text" name="name"><br>
                  Email: <input type="text" name="email"><br>
                  Phone: <input type="text" name="phone"><br>
                  <input type="submit" value="Submit">
              </form>
          ''')
  
      return app