In an interview with Huffington Post, Hank Azaria, who played David, revealed that it was never the plan for Phoebe to marry Mike.
"No, I didn’t know that was the end of David," Azaria said about his character's trip to Minsk. "The plan always was kind of to bring him back."
"I think, honestly, what happened was Paul Rudd is so awesome that they sort of found a groove with him and [my character] became more of just the grist for that mill as opposed to the other way around."
Azaria said that, given the choice, he would have preferred that Phoebe marry David.
“Whatever part of me is David the science guy who went to Minsk, which admittedly is probably a small part of me [laughs], but that part of me wanted to end up with Phoebe. So I was sort of sad when I didn’t.”
Looks like Phoebe still has guys fighting over her!