Theme my Login plugin, how to update fields

I’m using the Theme my Login plugin for a client project and I’m having trouble updating profile fields once a user has been registered;

I followed the instructions here but they didn’t seem to have any effect. If anyone could shed some light on it that would be great.

This is my current code;

register-form.php

<p>
    <input
      type="text"
      name="phone_number" 
      id="phone_number<?php $template->the_instance(); ?>" 
      class="input" 
      value="<?php $template->the_posted_value( 'phone_number' ); ?>" 
      size="20" 
      tabindex="20" 
      placeholder="Phone Number"
    />
</p>

profile-form.php

<p>
    <input 
      type="text" 
      name="phone_number" 
      id="phone_number" 
      value="<?php echo esc_attr( $profileuser->phone_number ); ?>" 
      class="regular-text" 
      placeholder="Phone Number"
    />
</p>

theme-my-login-custom.php

function tml_user_register( $user_id ) {
        // Phone Number
        if ( !empty( $_POST['phone_number'] ) )
            update_user_meta( $user_id, 'phone_number', $_POST['phone_number'] );
}
add_action( 'user_register', 'tml_user_register' );