PHP is not so good. First, ultra bad multithreading, nad cUrl-multi is a tiny funcionality in concurrency which gives you almost nothing. Also, whole error-handling pipeline is a mess - with PHP, you can write bot in some propabilistic way like, queuing task and then, veryfying all of them - I can't count how many PHP solutions i saw in ma career where creator thought that it just works, maybe with 90% efficiency, but the truth was that it was less than 2-3%. You can have many silent problems with PHP, and it is hard to catch/handle/log all errors in single place, it is very unconsistient and you should always write another bot to verify your primary bot work. In other languages, where all possible errors are thrown as exeptions it is a lot better.
Also real time monitoring is almost impossible in PHP - you can store status in database and monitor it from for example web page - huge workaround and definatelly not real-time.
And definately, not compiled languages (Java is) will be much much much slower, sometimes killing your possibilities (captcah decoding, DOM/HTML parsing etc etc).
Also you can forget about GUI in PHP, and embedding web browser in your application, also you cannot simulate "real mouse" clicks, only some web events with selenium server, which also restricts Bot writing possibilities.
So, definately we can say that is not a good language for writing:
-reliable
-functional
-fast
bots, only some tiny scirpts to scrap/post simple things, or use extarnal simple apis, with small reliabiliti/monitoring capabilities.