How alumni interviews are usually scheduled ? by email or in a phone call?
Is it a problem that I’ll be abroad for the next week and be unavailable in my phone but available in email ?
And is there a way to approach the university and ask about the interview? just to make sure they are not forgetting me.
Whether contacted by email or by phone depends on who the interviewer is.
If being contacted by email, just inform the interviewer of your available/unavailable days. If you get contacted by phone while you’re abroad and have no access to your phone, then just forget about it and check your phone for any messages once you get back. One week of no communication won’t hurt you, and there’s a good chance that the interviewer won’t contact you this soon.
Don’t contact the university at this point. It’s still early. See if anyone in your immediate area has been contacted for an interview. That ought to give you some indications.