Corrected entry: During one of the Las Vegas episodes Phoebe insinuates that she has been married in Vegas before. We know she divorced Duncan, the gay ice dancer, but we never hear mention of her divorcing this mystery man she supposedly married in Vegas. In season 10 she marries Mike Hannigan, so this would be an illegal marriage and make Pheebs a bigamist.
Corrected entry: In the episode where Phoebe's grandmother keeps lying to Phoebe about her father, Phoebe goes to visit her father and tells Joey and Chandler that, 'What if he's not this great dad. What if he's still the same guy who ran out on my mom and us before we were born.' But in the episode where Phoebe meets her dad at her grandmother's funeral, her father talks about how he burnt the formula, and put on Phoebe and Ursula's diapers backwards. Thus Phoebe and Ursula must have been born before Frank left.