Download termux on Google play (termux download)
In order to see your opened port you'll need mnmap. To download it just open a new termux session and type the few next's commands one by one.
Dont forget to press enter and wait until you see this sign ($). Once it's done type the next command
pkg install curl
Wait until you see the dollar sign and then type the last command.
pkg install nmap
If the installation is successful you can go to the second step.
The second step is very easy, just click on the link and copy your ip address. (The big blue number). (link for your ip)
Get back on termux and type this single command.
nmap -Pn (youripaddress)
You must not type (myipaddress)
The command should look like this:
nmap -Pn 99.999.99.99
(this is not a real ip)