For those saying she doesn't have a baby bump of any sort means nothing. People have been pregnant and not knowing they are pregnant until they start giving labor. Hell, I had a cousin who was pregnant for months and she only found out when she did her yearly check-up at the doctors and the blood tests came back telling her she was pregnant for a few months. Honestly, we will never know if she is pregnant until the day she goes into labor and has the kid. At that point, Phil wouldn't be able to hide a yelling child in his streams so he will tell his fans the day the kid is born. Plus, Phil won't mention the pregnancy ahead of time because he knows it will stir up shit like how he thought his life would be worse if detractors found out he was planning a marriage. Personally, I think this pregnancy theory is just that, a theory.
The only "evidence" we have is that both of them are going to the doctors, which is odd because for years Phil mentioned he can't afford to go to the doctors. Even then we can say that Phil's marriage allowed him to get on Kat's health insurance that she got from her job, so he is taking the opportunity to get a check-up which he needs. Or that Kat grabbed Phil's balls with a vice grip and demanded that they get health insurance because she wants them to be healthy, so he caved and listened to his SOULMATE.
The other "evidence" is cleaning out the nook in his house is him cleaning it up for a baby room or making it to Kat's new "office" since the baby would get Kat's old "office" since it's bigger and has a window. Even then that could be Kat demanding Phil to clean that nook up because she doesn't like wasting that space for his dumb toys, and rather use it for a cat room or some other dumb reason. Either reason it really means nothing but just speculation.
The last "evidence" is that Kat looks chubbier, therefore she has gained baby weight. Yet again that could be her eating more and not doing much at the Jim, as there are people who go to the Jim but don't really work out but just do 30 minutes of walking on a treadmill. Plus, like many people said we don't have full body pics of Kat except when she first moved in which we cannot use to compare her from her wedding pic as maybe she just got bigger from the move.
So until, we get more concrete evidence from Phil or Kat, like him slipping up on stream and mention something related to pregnancy, I say don't spend too much time on this. If anything we should make a betting pool on whether she is pregnant and when the hellspawn will be born.