Database Normalization .... But A PHP Question

Hopefully a quick answer for a quick question. I was reading and trying out Database Normalization but I don't think I get some of it with using PHP. I'll show my examples.

Without DB Normalization:

CREATE TABLE Users (
  user_id INT NOT NULL AUTO_INCREMENT,
  firstname VARCHAR(25) NOT NULL,
  lastname VARCHAR(30) NOT NULL
  email VARCHAR(80) NOT NULL,
  phonenumber VARCHAR(16) NOT NULL,
  PRIMARY KEY (user_id),
  UNIQUE INDEX (email)
) ENGINE=INNODB;;

Now, in php you would have a form with all the input elements. Then you would have a script that would insert those inputs into the database. ie:

$sql = "INSERT INTO user (firstname,lastname,email,phonenumber) values ('$firstname', '$lastname', '$email', '$phonenumber')";

Now With DB Normalization

CREATE TABLE Users (
  user_id INT NOT NULL AUTO_INCREMENT,
  firstname VARCHAR(25) NOT NULL,
  lastname VARCHAR(30) NOT NULL
  email VARCHAR(80) NOT NULL,
  PRIMARY KEY (user_id),
  UNIQUE INDEX (email)
) ENGINE=INNODB;;

CREATE TABLE PhoneNumber (
  phone_id INT NOT NULL AUTO_INCREMENT,
  pnum VARCHAR(16) NOT NULL,
  PRIMARY KEY (phone_id),
  UNIQUE INDEX (email)
) ENGINE=INNODB;

There obviously would be a foreign key in the PhoneNumber table for Users(user_id)

But how would I use the normalization in php to have the same 1 form but input the firstname, lastname, email into the first table and then the phonenumber in the next?

I know when selecting them both to be shown in site you would be joining the tables.