We don't know the exact day Leanna left Phil, but he must have been searching for a replacement immediately and especially after everyone starting dunking on him when he publicly announced the breakup on May 31, so it's entirely possible Phil was already at least vaguely aware of Kat by the time he first messaged her on June 1. The fact that he was able to convince her to stop streaming that same day and stop tweeting within the next few days shows that he went all in with Kat from the very beginning and more importantly how desperate he was. From Kat's perspective, it would have made some sense because the most viewers she ever had on a stream was like 5 and her tweets didn't get any attention either. Even if things didn't work out with Phil, she could just go back to streaming if she wanted and literally nobody would have noticed she was ever gone. What she didn't count on was getting caught and thot patrolled by Subaru Man, at that point she didn't have much of a choice but to keep going with Phil. Not exactly the most normal or romantic way to meet... But hey, SOULMATES!