You want to know more ?
Some webshells

https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Methodology%20and%20Resources/Reverse%20Shell%20Cheatsheet.md

Pure php Webshell: php-reverse-shell.php

https://github.com/pentestmonkey/php-reverse-shell/blob/master/php-reverse-shell.php

Yop Webshell: yopwebshell.php
Yolo Webshell: yolowebshell.php