The most active fork AFAIK is this one: https://github.com/andig/carddav2fb (with PHP8 support).

Features:

• Allows to import CardDAV-based VCard contacts (e.g. from 'owncloud') to a phonebook in a AVM FRITZ!Box
• CardDAV import includes photo images specified in VCards
• No modification of FRITZ!Box firmware (aka FRITZ!OS) required
• Definition of multiple CardDAV accounts and "folders" possible
• Format of full name in FRITZ!Box phonebook can be designed

CAUTION: This script will overwrite your current contacts in the FritzBox without any warning!

• PHP-version 5.3.6 or higher
• PHP-curl module
• PHP-ftp module
• PHP-mbstring module

Checkout the carddav2fb sources including its related subprojects using the following command:

git clone https://github.com/carlos22/carddav2fb.git

Now you should have everything setup and checked out to a 'carddav2fb' directory.

1. Make sure you have System -> FRITZ!Box-Users -> Login via Username+Password in your FRITZ!Box activated.
2. Make sure you have a separate user created under System -> FRITZ!Box-Users for which the following access rights have been granted:

• FRITZ!Box settings (required to upload telephone book data)
• Access to NAS content (required to upload photos via ftp).

3. Make sure the telephone book you are going to update via carddav2fb exists on the FRITZ!Box, otherwise the upload will fail.
4. Copy config.example.php to config.php and adapt it to your needs including setting the FRITZ!Box user settings.

1. Install PHP, PHP-curl, PHP-ftp, PHP-mbstring and php-xml module:

    sudo apt-get install php-cli php-curl php-ftp php-mbstring php-xml
   

2. Open a Terminal and execute:

    php carddav2fb.php
   

1. Download PHP from php.net. Extract it to C:\PHP.
2. Start -> cmd. Run C:\PHP\php.exe C:\path\to\carddav2fb\carddav2fb.php

$config['fritzbox_ip'] = 'fritz.box';
$config['fritzbox_user'] = '<USERNAME>';
$config['fritzbox_pw'] = '<PASSWORD>';
$config['phonebook_number'] = '0';
$config['phonebook_name'] = 'Telefonbuch';
$config['fritzbox_path'] = 'file:///var/media/ftp/';

// full name format options default 0
// parts in '' will only added if existing and switched to true in config
// 0 =  'Prefix' Lastname, Firstname, 'Additional Names', 'Suffix', 'orgname'
// 1 =  'Prefix' Firstname Lastname 'AdditionalNames' 'Suffix' '(orgname)'
// 2 =  'Prefix' Firstname 'AdditionalNames' Lastname 'Suffix' '(orgname)'
$config['fullname_format'] = 0;

// fullname parts
$config['prefix'] = false; // include prefix in fullname if existing
$config['suffix'] = false; // include suffix in fullname if existing
$config['addnames'] = false; // include additionalnames in fullname if existing
$config['orgname'] = false; // include organisation (company) in fullname if existing
	
$config['quickdial_keyword'] = 'Quickdial:'; // once activated you may add 'Quickdial:+49030123456:**709' to the contact note field and the number will be set as quickdialnumber in your FRITZ!Box. It is possible to add more quickdials for one contact each in a new line

// first
$config['carddav'][0] = array(
  'url' => 'https://<HOSTNAME>/remote.php/carddav/addressbooks/<USERNAME>/contacts',
  'user' => '<USERNAME>',
  'pw' => '<PASSWORD>'
);

This script is using third-party libraries for downloading VCards from CardDAV servers based on the following packages

• CardDAV-PHP (https://github.com/jens-maus/CardDAV-PHP.git)
• FRITZ!Box-API-PHP (https://github.com/jens-maus/fritzbox_api_php.git)
• VCard-Parser (https://github.com/jens-maus/vCard-parser.git)

This script is released under Public Domain.

Copyright (c) 2012-2016 Karl Glatz, Martin Rost, Jens Maus, Johannes Freiburger