To open the 2 1 port of a mobile phone, it is necessary to confirm whether the port is used by an application. Port 2 1 is usually used for FTP (file transfer protocol) service, so it is necessary to ensure whether there are related FTP applications using this port. Secondly, you need to make sure that the firewall of your mobile phone is turned on. In Android phones, most firewalls are open by default, but some applications may require users to manually open firewalls to open ports. By opening the firewall, external devices or networks can be allowed to connect to the 2 1 port of the mobile phone.