This is no way a hard requirement for PhD application, at least in the US. I didn’t have any accepted first author conference paper when I was admitted (senior year). I was still accepted to a few T20 PhD program. However, I did get 2 first-author papers published by the end of senior year, one was a workshop paper and one was a conference paper with Honorable Mention. You’ll need to have some research experience, do hard work and really impress your advisor. Hopefully, you will come up with some publishable ideas. I think the key for direct admit is having your advisor really vouch for you in their LORs. Getting a paper accepted is also a matter of luck, so having a professor saying that you produced high quality work is a good alternative.