Most likely by attacking the phone itself. That is the easiest way
⚡️🇷🇺 NEW - Putin’s spokesman Dmitry Peskov says all messaging apps, including WhatsApp, Telegram, and Signal, are fully accessible to spy agencies:
“Any messengers are absolutely transparent… for the security services, of course.”
https://blossom.primal.net/61681d2bd450889807b66a98f15352a46d90a2b84a994b3d7df39fff5d97de3d.mp4
Discussion
Yeah exactly it’s a leaked IMEI plus some kind of zero click.