my phone was dead for about 30-45 minutes and my boyfriend called multiple times but each time it went through and rung as if it was on. why did it do that?

That would be normal. Your phone, whether off or on, would still ring to a caller, and they would be able to leave you a voicemail message if you have voicemail, because the call is handled on the carriers network.

That's a question for your carrier. They handle phone calls.

If the phone is off or “dead”, the caller will hear the rings before it goes to the voice mail. Is that what happened?