The foreign companies are basically criminal operations and countries like the US have taken action against them in the past by working with local law enforcement[1].
[1] https://www.scmp.com/news/asia/south-asia/article/2179175/mo...
Having said that, these people will also give their phone number and email address to anyone who asks whereas I do not. If I have to enter a phone number on a form and it's isn't immediately obvious why I should do that then I'll make-up a number.
- people giving their phone number out to companies that share this data, and
- people answering spam calls. Even if you hang up immediately, they probably have an internal metric that says call that number back more frequently.
I don't do either of those, and last week I had more spam/unknown calls than usual: 4
For online forms that require a phone number, I just insert that company's own number.