ReginaldGupta
Has this always been the case, or did it start happening suddenly (maybe your phone number was exposed in a data breach)?
Using the AOSP built-in features, you can block all numbers that come without caller ID and/or aren't in your contact list:
Phone app > Blocked numbers- toggle on Numbers not in Contacts and Unknown.
There are also apps available to block spam callers. I don’t use any of these apps, so unfortunately I can’t make a recommendation. But you might find this discussion helpful, for example:
https://discuss.grapheneos.org/d/27726-which-app-can-you-recommend-for-blocking-spam-calls
The most inconvenient but also most effective solution is probably to change your phone number.