No, Ben Geller was not Phoebe Buffay's son.
Ben was the son of Ross Geller and his first wife, Carol Willick. He was born during the first season of the popular sitcom Friends and frequently appeared throughout the series as Ross's child from his initial marriage.
Phoebe Buffay, a beloved central character in Friends, did not have any children of her own during the show's entire run. While she played a significant role in her brother Frank Buffay Jr.'s family by serving as a surrogate mother and carrying triplets for him and his wife Alice, these children—Frank Jr. Jr., Leslie, and Chandler—were not biologically hers, nor did she raise them. Her relationship with her husband, Mike Hannigan, also did not result in biological children for Phoebe within the series timeframe. Ben was exclusively known as Ross's son.
