Phoebe got an extension that allows it to host capsules – these are not the wiki spaces it usually hosts, but single-user spaces. You are assigned a space based on your client certificate.
If you visit the site and you have a client certificate active, you’ll see the link to “your” capsule. Go there and upload files or edit gemtext files using Titan, i.e. using Lagrange.
What happens is that you visit the site and it generates a username for you, based on your client certificate. The common name in your certificate does not matter. You are assigned a name and you cannot change it. You can change your client certificate and you’ll get assigned a new name, but that’s it. Only you can edit your capsule (but there’s a way to share access).