The thing is Stephanie sees herself as an empathetic and good person. She gives 'love' back and does charity work, the motivation behind these actions are just different from normal people. She does it to assert control and secure a source of adoration (love for Phyllis) and personal thank you's and admiration to feed her narcissism (GAG). She's completely unaware of her real motivations behind her doings, that's the narcissism, she's not manipulating people consciously (that would make her a psychopath, she's not), the reason why she seems genuine to some that aren't as perceptive as us.
I think Frank wants an explanation from her he could accept and agree with. There's no such thing.
You're right, we're giving her attention here which she appreciates. She thrives on any attention. We're challenging her, she gets a reaction from us. We could of course gaslight her back and beat her in her own game, feed the flames of her crazy, insert poison needles in our comments to keep her insecure and encourage her to overstep promising even more adoration in return. But we're decent people, we don't like to see people suffer. Not even her.