FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 192295

This article explains how to change the admin default port to the custom port to avoid conflict.

In many cases, reach the FortiGate unit with ping, Telnet or SSH is possible.
Reach the GUI doesn’t work due to change in admin default port.

To access the FortiGate with the admin login via GUI, port 80 is used for HTTP and 443 for HTTPS (by default).

If these ports are changed or intended to be changed, refer to the details below:

1) Verify the current admin ports configured for admin access.

#show full | grep admin-sport                                                                                   <----- verify https port.
          set admin-sport 443
#show full | grep admin-port                                                                                     <----- verify http port.
          set admin-port 80

If the ports have been changed, use the below url to access the GUI:

http(s)://<IP of the Fortigate>:<custom port>

Example: where 300 is the custom port configured to access GUI via HTTP.
Same applicable for https access as well.

For changing the admin ports, use the following commands:

#config system global
    set admin-port <integer>                                                     <----- for http access.
#config system global
    set admin-sport <integer>                                                    <----- for https access.