I once heard that if a number that you don't know called you, you can access a website (that I don't remember now) that will call the number and make a recording of what the person said and send it to you. Is it legal? Or can I find a better way to find out the person identity?
Why are you assuming it is a "person" who called you?
Most people will just Google the number - typically if this is one of those spam callers you will find out some information about them on discussion groups.
I am not sure why it would be illegal to search publicly available information about a phone number that called you.