Remember the IP used in home is not the one used when not at home.
you need the IP of the router and the Port number being used by the cam when outside.
Have you tried to see what the I-Phone is using when not at home. It has to be an
IP and port to get to the cam. Regardless of the app used on the cell phone it has to use an IP and port to reach the cam and not the internal home IP addresses.
this may help,
go to this site and it will give you the IP address your router is using on the internet side. https://www.whatismyip.com/
once you know the external IP address and you know the port number the cam is using ( as shown in the Amcrest configuration )
try using your call phone browser to see if it is accessible http://188.8.131.52:8000
( example )
your IP will be in place of the 184.108.40.206 the port will be what you see in the configuration.
you can also find the port by logging on to the home router and see what port the cam is using or assigned to.