LMAO. Well... Let's see...
Fair warning: Long time Phantom fan, but, I've had the time to max the bad boy 1 x Balanced Mod, 2 x HAKs, AH active module, maxed legendary pilot. I was a big fan of tasers on Phantom, buuuu-uu-uuut, because of frickin' Shells I switched to flames.
Pros of flames:Slice right-through Shell shields like a sharp slicey thing through a warm, gooey thing. Because I use suppression chip(s) it can really ruin their day.
Penetrate blue/ancile shields. (Admittedly, like most things.)
Hard hitting. Once they reload you are doing 100% damage out to 350m.
Already been through buffing/nerfing shenanigans and they are good as-is.
Flames don't need to lock-on like tasers. They don't need a pilot skill to make them better. And Flames don't need a participation trophy.
Accumulate effects like suppression pretty well.
A little more range than Sonics, which can help here and there.
Cons of Flames:Can be quite tricky to aim especially at a laterally moving target at 300m.
350m isn't the best range ever. Good enough I guess.
Cons of Cryos on Phantom:If you play beacon games I'm no fan of freezy-rockets on Phantom. You dash in, give'em hell, and then pew-pew or Blink back. Giving them the beacon. Cryos on a Nightingale are a blast, but not Phantom. Don't sell your leveled Cryos for a paltry amount of Ag, they are still worthwhile.
FWIW, Phantom isn't uber-meta anymore but I run it as a quick beacon runner and I'm too stubborn/poor/smart to run a 2 x Demeter, 2 x Shell, 1 x Hawk hangar. The Phantom will just have to work for now.
I hope this helps. Good hunting!