input: Write a function to create a Flask application that allows users to submit form data with fields for Name, Email, and Phone, and stores this data in an SQLite database. The function should return the Flask application object.
  
  assert create_flask_app()!=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 '''
              <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