Just as the title says, I haven't done a whole lot of PHP, but I know that you can set up websites that accept HTTP Post requests with it, so I was wondering if it's possible in a plugin (I assume it is because vote plugins need to work somehow, right?) and if so, how? (I'm mainly a Java plugin developer, I make private plugins for servers, but I have a client who runs a Pocketmine server and I need to know if this is possible, thanks.)
You can have the plugin create a webserver, however that'll break it on almost every Minecraft server host as they'd block all ports but 19132. Most vote plugins just periodically query an api (example). If you need fast bidirectional, remote, communication consider using a tcp socket.