+1 to the last few respondents except the last one.
With reservation for using public phone. Remember that when you or the reporter is on the radar, they will record your voice signature, then they will search all networks for a match. In couple weeks they will know who you are.
The correct procedure is to get cheap phone/SIM as described above, buy airtime - all cash, then search the reporter's phone number on Telegram or Signal (or other secure messaging apps, but not WhatsApp, as reporter's WhatsApp account could be cloned), make an appointment in the pub (wearing sunglasses / hat and a fake mustache) of your choice using secure chat. You must be a known physical person to the reporter with your permanent contact number and address, otherwise your story has no chance to publish. Don't play anonymous to the reporter, it won't work.
When you finish your business, private sell or dispose the phone with SIM.