I know this is a little late but this is what I used for Rom on NG++ Get a fast weapon, but it has to be buffable (I used a +8 Rakuyo wich honestly had low damage but it did just fine) and a strong weapon to kill the spiders in 1 hit (I used Chikage). Kill all the spiders around Rom until she is the only one left. Next, get you fast weapon, eat a Beast-Blood pellet, buff your weapon with bolt papers and spam-attack the ***** out of her. Using this I was able to simply skip phase 2 and went directly to phase 3 with her only having a little bit of health. I she isn't dead, you can play safe killing all the spiders or just rush her. I also used full Choir set so I could focus on killing spiders rather than dodging Rom's attacks.