Phoenix on lotus is basically just playing for flash zones (defense) and ult orb farming (attack). Generally starting b on defense is pretty good on phoenix. Woohoojin has uploaded a video for phoenix (https://www.youtube.com/watch?v=ILfNAOKlbIM) and it seems like most pros start b main to play for his flash and molly to control that space. Playing middle of the map is also pretty good if your teammates are playing the map incorrectly and allows you to fast rotate to either site.
My general pointers for improving :
-You rush your shots, especially after flashing. Round 3 showcases exactly the effect this has, as you fail to kill jett before they kill your neon. Also the last round of the game you completely whiff on the full blind chamber and he kills your clove for free and it almost loses you the round.
-You need to play your flash more, its almost the only reason anyone plays phoenix and its the only reason hes viable on lotus. I really think that the order of improvement is Mechanics, Agent Skill, then Teamplay, and then refining those until they are perfect. You need to understand your role and what plays/positions provide the most value to you and your teams chance at winning the round/game. For example on round 3 you play c link which I think no duelist ever would play at because it doesnt make sense. Up until you fight the jett, you are providing no value to your team. You are not a sentinel, you need to be in a place where you are fighting/able to start fighting/threaten to start fighting.
You will likely have a hard time getting better on phoenix because there is no good resources for improving at phoenix and also because phoenix really doesnt fit into team dynamics very well besides just being like "phoenix flash op lol" or "farm orb easy win"