Do not call them directly.
One of the reasons for HR departments and recruiters to exist is that they are supposed to handle your application, and the point of a phone interview is to get a quick gauge of a candidate without spending too much time on every applicant. Whoever called you for your phone interview called you only for that phone interview, and will not want to be hassled with further unsolicited calls from yourself, when they might be in the middle of something else - unless they explicitly told you that you could.
All else being equal, the most likely reason they've not got back to you is that they have decided not to continue with your application for some reason. (This may not be as a result of anything you've done wrong - they may simply have already filled the position). It is impolite of HR not to respond to your calls, but that kind of rudeness to an unsuccessful candidate is, sadly, not uncommon.
However, if HR are not responding to your attempts to follow-up...
If HR have not responded to your calls and emails for a significant length of time (definitely more than a week - at least two would be better - their HR staff may simply be on holiday for example), it is possible that something has gone missing between the interviewer and you, and it might be worth finding another way to follow up. (Note the disclaimers. This is possible, but less probable than that you're not still being considered).
In that case, you might consider sending an email to the interviewer if you have their address, or can find it on a public site (e.g. the company's website, or LinkedIn). Unlike a phone call, this places no demands on their time (they can just press "Delete" if they don't want to talk to you) so even if they find your persistence annoying, it will be low-level annoyance and forgotten quickly.
Do not try to "guess" at their email address or start looking up their non-business social media profiles. If you can't find their email as public company-related information, they clearly do not want to be contacted and you should not do so.