Hey Ellie (I presume that's your name),
Indeed you can apply for multiple PhDs at the same time. In fact, if you are certain you want to do a PhD, it would probably be a bit silly not to, assuming there's a few you are interested in. Some application forms may ask about other unis/projects applied for. People on here sometimes ask whether it's best to say what else you're in for, or keep quiet. Personally, I think that, as long as the range of projects isn't huge, tell the truth - after all, if you're the best applicant, they won't reject you just because you've applied for other projects. They may, however, want somekind of assurance that, if you accept their place, you won't then take another. Whether this in enforcible is another question...
If you apply for one, and then leave others until you get a final decision, you may miss the boat on other projects you like the look of, so apply for what you want, and good luck!