Well, that's what happens when you whip yourself into a corner. Phil was so humiliated after Leanna left him that he's decided to throw his money around to keep Kat from leaving because that's literally the only thing he has going for him. At the very least, we know he bought her a whole new wardrobe and brand new furniture when she moved in. However, there is a counter-argument for this: their lives still revolve around Phil's autistic schedules and creature of habit lifestyle. She has to be home to cook him his microwave dinner and listen to him whine about trolls, she has to go grocery shopping with him on his designated day off, she's been dragged on streams numerous times when she clearly didn't want to, and as far as we know he's only taken her to places he took Leanna to previously (Space Needle, IKEA, zoo, Vinny's, etc.). I think it's more likely Phil plays the "I pay for everything, do what I want!" card than she plays the "Buy me this or I leave!" card. I don't know, it's hard to tell because their relationship is a total sham. The power balance between them shifts depending on the circumstance.
No way. He'd have to get a lawyer to write up the NDA (expensive and time-consuming) in addition to handing over a presumably large lump sum or monthly payment of money to Leanna. And if he did break the NDA, she'd have even more incentive to go public with Phil's dirty laundry, to get more money from him. Here's the reality: Leanna wants to move on from the mistake that was her 5 year relationship with Phil and be her own person. Who could blame her? The less she's connected to a shithead like Phil, the better.