PHP is Turing complete, so it's technically possible to write anything in PHP that you could write in another language. That seems to be about the most it's got going for it. PHP does nothing to help programmers write sane, maintainable code. It's almost impossible to develop without having a browser tab open to php.net ("The online docs are great!" "Well, they'd have to be."). There is zero consistency with things like argument order. Dangerous legacy concepts like "mysql_real_escape_string" are only recently deprecated and don't have a set removal schedule. It's a one-trick pony that's nearly useless outside its niche as a web page generation language. It's just a mess - a dangerous, unmaintainable mess.
I won't refuse to use an app just because it's written in PHP, but I do heavily weight it when comparing alternatives. PHP is a powerhouse in much the same way as McDonald's. It may be ubiquitous, but it still sucks and you have to question the judgement of anyone who chooses it to start a new project.