I can't link Brave Browser to my Uphold account in my phone

You must have not filled out the form properly. If you currently have a device that is linked that you want to keep linked, you need to put that wallet info in the form. They will then unlink one of the other devices. I followed the instructions and a few days later, I was able to link another device. They can currently unlink 1 device per request. When you try and link a new device after that, make sure you are following all of the steps on the device you want to link. Turn off vpn and brave shields too.