If a PhD position I applied for and didn't hear back from is removed and relisted, does this mean I was rejected?
Reposting a search does not mean that all the applications received so far are unsuitable. It often means that they have not received the volume of applications they expected/wanted and are worried, without having necessarily looked at the applications, that they might have missed qualified applicants.

Given you applied on line and never got a status update, it is always reasonable to ask if everything is okay. Given the position has been reposted, it is worth asking if you need to resubmit your application. Sometimes HR and electronic systems do not carry applications over from one position to the next.