If you are interested in being a PhD student under my direction, then a necessary first step is to apply and be admitted to the Mathematics Department at the University of Florida. Admissions are done at a department-wide level, and here are the application instructions: https://math.ufl.edu/graduate-studies-in-mathematics/admission-to-the-mathematics-graduate-program/. Many further questions should be directed to the email address listed there: math-gradapps@ufl.edu.
Applications are due in January every year, and then admissions decisions come out in the following months. Let me know if you have any questions regarding the application process, and you can certainly include my name in your cover letter. Admitted students are almost always granted funding through teaching duties.
In mathematics PhD programs in the US, advisors are typically chosen within the first two years, but it can be valuable to know in advance who you might work with, and the current sizes of their groups. So, you should certainly let me know if you are accepted to the University of Florida, since we could touch base then.
Also, you may be interested in joining AATRN’s online events, or its email list for online talks:
www.aatrn.net
https://groups.google.com/g/aatrn