How do I access my laptop’s files from my phone?
Tailscale only provides a secure connection between your laptop and your phone.
It is then up to you to run a service the exposes your files over that connection.
As an example, python provides a simple HTTP file server out of the box (https://docs.python.org/3/library/http.server.html). So you could change into a directory that you want to share, and run:
python3 -m http.server 8000
and then only your phone, browse to http://LAPTOP_IP_ADDRESS:8000/