geb2
Not my phone. My parent's smartphone did that, calling the phone of the other parent around 2 months ago. They have some old Android devices (not Pixels, not GOS) that are long end-of-life.
I have seen thousands of pieces of evidence over the last 6 years that all devices are hacked in our house. Not 100% of them are, of course, correct, as can be seen above, but I'd say around 99%.
In your case, it's important if you have actually witnessed that your smartphone is actually calling somebody's phone on its own. If not, this can be some other thing, such as SIM spoofing, as it was pointed out above.
Check out this link: https://www.fcc.gov/consumers/guides/cell-phone-fraud
If you haven't seen your smartphone actually calling some number without your action, then your device is very likely to be clean. If you have it, then I don't know what it is. You cannot check it if it's compromised on your own; you'd need to get some digital forensics done, and even then there is no 100% guarantee. Anyway, most people say these devices are very secure.