Sometime after the events of TFA, Phasma is set to be executed by the First Order for treason for lowering Starkiller Base's shields. Phasma makes a snap decision and ends up running--and getting caught by the Resistance, who wants to keep her as a POW/use her as bait to lure out the First Order. Finn however shows her compassion and kindness, argues for her release, leading to an unusual relationship between the two (whether or not its sexual/romantic, platonic but co-dependent, or like Phasma just going around beating up everyone on-base who looks at Finn the wrong way, I'm not too picky).

All I really care about is Finn being kind and compassionate towards her despite what she did to him when he was in the First Order, and his other friends (Poe, Rey, Leia, pilots, etc) not understanding the relationship, nor trusting Phasma.