If you want to block this application, you will must to block all VPN which are not yours. You may read about Psiphon for PC here or just follow the steps below to unblock the app:--
1. Enable DPI-SSL Client Inspection by going to DPI-SSL | Client SSL and selecting Enable SSL Client Inspection. Ensure that IPS, GAV, Spyware, and Application Firewall are selected.
2. Enable all Psiphon application signatures by going to Firewall | App Control Advanced. Select the category PROXY-ACCESS and application Psiphon. Configure the application to be blocked and logged.
3. Also block Encrypted Key Exchange TCP Random Traffic (SID 5).
4. Enable blocking of SSH app signature (SID 10097) "SSH -- Client Request Outbound", (or make access rule to block outbound TCP/22 SSH Service from LAN->WAN).