Sure! I can offer my interpretation.
So, this scene starts off with Ellen having gotten anxious enough about the FBI investigation into Larry to voice her fears and frustration and suggest they take a break, right. When they’re talking about it being a phase, I don’t think Ellen even thinks that, she just grabs onto it in the middle of their argument as a possible escape, a fantasy, because otherwise this FBI thing, in one way or another, is her whole life. She originally sat up to resolve this unease by either being reassured or instigating a breakup, whichever way it ends up going.
When she says that she feels like a different person with Pam, she means it in the sense that, oh, this is “normal” me and now this is the dangerous part that likes a woman at all. She’s just talking about sexuality. But Pam means it in the sense that there’s the regular non-loving Ellen part and the loving-Ellen part as the two different versions of her, she doesn’t just mean sexuality, she’s narrowing it to Ellen specifically, making it suddenly deeper and more romantic and like, signaling a shift in their relationship, something more meaningful and committed and long-term. She knows that’s clear to Ellen too and kind of challenges Ellen, considering the conversation they’re having, if that scares her and Ellen’s “no” means, on some level, accepting that shift, instead of pulling away. So it’s a big step forward for them and Pam is, I think, emotional and pleased about it.