input: 
  from flask import Flask, render_template, request, redirect
  import sqlite3
  
  app = Flask(__name__)
  
  @app.route('/')
  def home():
   return render_template('index.html')
  
  @app.route('/submit', methods=['POST'])
  def submit():
      """Submits the form data to the database. The form contains three elements: name, email, and phone.
      After submission, the user is redirected back to the homepage.
      
      Example:
      >>> submit()
      Redirects to the homepage after inserting the form data into the database.
      """
      name = request.form.get('name')
      email = request.form.get('email')
      phone = request.form.get('phone')
      
      conn = sqlite3.connect('data.db')
      cur = conn.cursor()
      
      cur.execute("INSERT INTO data (name, email, phone) VALUES (?, ?, ?)", (name, email, phone))
      conn.commit()
      
      return redirect('/')
      
  if __name__ == '__main__':
      app.run(debug=True)
  
output:     conn.close()