1st - You are wrong! The Pool is not in the basement - The basement is the room where Monica lives and sleep in the house and if you not choose every time some of the "fast icons" in your right corner so you can easily go to another room and instead that you just decide to leave the basement room you are going through a coridor where also have another a "dark passage" but it looks like Monica cant get go there yet and the other road it's to the "Laundry"....Once in the laundry room Monica can go through the door there and she find herself in the showers and the pool and from there she can go back to the laundry or decide to go through the second door and find herself in the "down floor" of the house! Even on your "fast icons" in your right corner it's placed the name of most of the places in the house: Bedroom;Bathroom;Ground Floor;Upper Floor;Street Yard;Laundry;Bassement(there are also other rooms who are missing in that fast icons like a kitchen,Bardi's room,lounge - but that's not the point)! So once again you are mistaken!
2nd - Well,i think Phillip used Monica there two times actually but i need to go play it once again to see if it was like that - But even if it's only once that's not the point - the point is that he was the one who used her in "basement" and not Steve!
3rd - Actually on that presentation you have a choice to who to turn - Monica can turn her back to Steve and let him has his fun or to turn her back to Philip and let him to enjoy the look and have fun...So here we can agree that this actually depends of the choice the playerd did