Worst case scenario - he may not answer or in negative or rudely.

Give it a try, nothing wrong in asking it. Make sure you are calling him/her during no-office hours. At least he will remember you for your courage and confidence.

Don't over think, and don't go by the rules of society / corporates.

If you've sent at least 3-4 mails at valid intervals and with proper application & follow-ups — and tried reaching out to the HR Id through mails and the firm phone number given on the website — then you could, in a formal office hour, make a respectful call if you're ultimately reaching a date extremely close to the internship period that you've applied for. Begin with a humble greeting, then apologise for disturbing them and ask them if this is a good time for a 5 minute conversation — they'll probably ask what it's about & who you are — and you ought to utilize this opportunity to give a summarized keynote-type formal & straightforward answer, while quickly adding the urgency & reasons for this being a genuine call. An example I could think of would be if a student called with this etiquette and clarified that they have been asked to confirm their slot for a different opportunity for the coming month — but they would (respectfully) prefer to get clarity about their application status from this firm first.

Remember, we're not anti-students; we've been students once too. But we're still professionals with a lot of work (& some life) and most students fail to respect any of that by reaching out clearly unnecessarily and being woefully ill-prepared. Just don't do that, and noone will hold a grudge.