If you have a pixel you can turn on call screening for unknown numbers. Ive been using it for a couple years now on my pixel and my phone hardly ever rings now, its fantastic
Phone > settings > call screen > automatically screen calls + maximum protection.
WhatsApp has a zero day code execution exploit and that is probably the reason for using WhatsApp, I got a similarly odd text a couple days ago
Source: https://gbhackers.com/zero-day-exploit-whatsapp-hacker-forums/