I really need to contact a professor by the end of this week, and I've already emailed them twice. Their automated reponse said that they would be back in the office in the first week of July, and so I was considering visiting their office, but I don't know the office hours (or if there are any during the summer). Would it be okay if I give the prof a phone call and leave a message? Or is that not a good idea?

Thanks in advance!

Maybe you can try calling the department they're in and asking what their office hours are first, and if that fails, try calling them directly.

It\s fine to call them, you can say you left many e-mails and they did not respond for whatever reason.

Keep in mind though, if the automated response says they are out of their office, dropping by their office or leaving a message might not be the most reliable plan of action. I'd definitely call the department first to see:

a) If someone else can help you
b) How that prof can be reached