Easiest way to access localhost from iPhone
Other than Ngrok, ssh.localhost.run is excellent for that purpose. You need to have the Openssh Client. Use :- 

ssh -R 80:localhost:port ssh.localhost.run


Replace "port" with the port your server is running on. You will receive a link,  just like Ngrok, you can use that link. Other than localhost.run there is also serveo.net, use it the same way as localhost.run, but it is currently down, so localhost.run.