How can I obtain someone else's phone record's

How is this person related to you?

Simple... you don't.

It requires a Subpoena from the court... and they are going to require a legally sound reason why you need them. I doubt you will meet that requirement.

Think at it this way....would you want just anyone else getting YOUR records easily?

The only legal ways. Ask them for them, or get a court order for them.
There is no way to get them otherwise

Usually this question is asked by someone suffering from extreme suspicion and jealousy of a spouse or lover. Is that the case with you?