I play Phoenix on a derpy team of Morrigan/Sent/Phoenix (you can obviously figure why Morrigan is on the team) so I can help out a bit.
Some of the strategies are kinda specific but the main thing you want to know is that you want to learn how to fight Phoenix. Just relying on snapping in doesn’t teach you how to fight Phoenix. It’s just the easy way out and top Phoenix players like Clockwork are learning ways around snap backs. The people who do best fighting Phoenix are the ones that can actually fight her and know where the spots to hit her are. The first thing you should always do is to try and snap her in and kill her but she can always escape with a well placed teleport when she figures you’re going to try and hit her which if you whiff something during she’ll end up hitting you and doing a tag combo and build more meter. Most Phoenixes you’ll encounter wont be good enough with her to mount an actual offensive with her so if u bring them in and just make a good read u should kill her off.
Generally the best things to know about fighting Phoenix is that everytime she throws a fireball or teleports she’s actually putting herself in danger. People just dont see this because she’s usually very high in the air when she does a fireball and the teleport appears very fast. Generally if you’re using a character like Magneto/Phoenix or Sentinel you can make things really rough for her. Her fireball has 20 frames start up and 20 frames of recovery so like with Sentinel you could easily catch her trying to throw a bad fireball even when she’s Dark Phoenix and get really close to killing her. Probably the easiest mode way to kill off a D.Phoenix is to have Magneto available with his Gravity Sqeeze that is only 20 frame start up and will freeze her in any spot in the air and instantly kill her if she starts to throw even one fireball. Storm can also do this with her hail storm but u have to do it a bit more premptively because it’s 40 frame start up. At the same time you can cut off the recovery of the hail storm by doing someone else’s super first then DHCing into her so the super will start up in 1 frame.
From there you’ll want to know that her teleports have like 20 frames of recovery. So this means unless the Phoenix player has a homing fireball on screen when they teleport you can just press jabs when u feel or see her teleport and hit her for free. Which is why most Phoenixes will try to throw fireballs first so you’re forced to get hit even if you hit her and then she can combo you. This is why your best bet if she’s not D.Phoenix yet is to just super jump and chase after her. If you get hit with a fireball when she’s in the air its not likely you’ll eat a huge combo because she wont risk comboing off it into super. Your main job in general with fighting Phoenixes is to find any method you can to stop them from throwing fireballs. If you can do that the rest of their game is a lot harder to apply.
This of course again becomes harder if she’s in level 3 X Factor but that’s really the whole point of the character. She’s supposed to succeed if she doesn’t die before 5 meters and never has to use level 3 X Factor until she turns into D.Phoenix. Supposed to any way. She still has 400k health and after the XF level 3 is over will still have to use healing factor to have any small chance of surviving after that.
The main strategy you want to have against any Phoenix player is HOLD ON TO YOUR X FACTOR. You’re going to need your level 3 X Factor to counter hers. If you waste your X Factor early you might as well just count yourself out . She wont even have to go near you to win. She’ll just be able to chip you with projectile normals, fireballs and traps all day. She even has combo loops off her trap fireballs so that’s the last thing you wanna be fighting against without level 3 XF.
You’ll ideally want to activate your X Factor after she does. If you can force a D.Phoenix to activate their XF in a situation where they dont combo into it (like just activating in the middle of the screen) this works in your favor. You’ll then be able to immediately react with your own XF level 3. You’re going to need this because a lot of D.Phoenix’s strength is that everything she has chips and she rapid fire you with chip. Which is why blocking feels ineffective against a level 3 D.Phoenix. When you get your level 3 XF activated it means she HAS to land a hit to kill you. She’ll be super powerful and super fast and have easy mode death touch combos but she wont be able to set them up without putting a ton of fireballs or traps on the screen that wont chip you. Plus not that you needed the damage help but it’ll make it so you’ll be able to kill her by sneezing.
If you can turtle counter her XF with your XF for 20 seconds then you’ll make things easier. Considering u didn’t find a way to land a hit which ended up killing her. At this point then she’s just going to have to go in and kill you and although non XF D.Phoenix is really strong she’s not quite the insurmountable force she is in level 3 XF. That’s what people are afraid of and I told people they would be afraid of. D.Phoenix without XF is basically dying just like she was in the comics with her health running down which means she’ll have to activate healing factor from a distance or find a way to combo into it if she gets near you revive her health. At this point you can just concentrate on finding a bad fireball or teleport and punishing her hard with a combo or super and generally the fact that her health is going down at this point will make things easier.