There are many ways with which you can send a fax and there are a few good options for receiving and sending a fax from your iPhone.
Fax burner
This app is also one of the most used apps as it is also easy to use and also this app provides no-cost charges up to five pages that you send by fax.
Ifax
It is one of the many apps that is being used for sending and receiving a fax from iPhone but this app is better than another app so it is recommended to use more than another app.
eFax
This app is also the most used app by iPhone users.