I have a form-like page in an iPhone page. Are we really required to put a Cancel button along with Submit button?
P.S: The user can go back by using the regular Back button in the left top corner.
The standard in iOS is
The general idea is (as far as I can tell) is that the edit pages (with back button) let you edit stuff in real time: going back means that all changes will be saved
And the modal pages work differently: pressing cancel means that any changes will NOT be saved.
You can press ready or back, in both cases your edits will be saved.
In iOS mail, you get a Cancel button in top left if you create a new mail. Cancel means "do not save" (or typically a pop up asking if you are sure you want to discard changes).
So in your case I would say:
You can leave it out, to the best of my knowledge Apple isn't so strict as to look through apps and say they can't be in their app store simply because they don't like the UI, so it isn't "required", but many would advise against it unless you have a specific reason, and you understand why it is common practice among the best iOS apps, including those from apple; you should understand rules before you choose to break them.
A couple things to consider include:
There are plenty of other things to consider, but you CAN make everything in comic sans and make the app's interface upside down; if your app's design is justifiably better for having done something differently, it's your call on whether you do that, but whether it's a good idea requires either more info, or for you to consider the implications of that design decision.
What is your objection to having the cancel button there? As long as the standard page Back control and it is clear to the user that they may use it, you might not need one.
However, if this is a form that the user may fill out part way and then decide to leave, having an explicit Cancel control is a bit more intuitive... just make sure to give them a "dirty save" message as well before canceling if they've filled anything out; something along the lines of "Canceling will abandon any changes you've made to this form; are you sure you want to do this?"
I don't know if there is a requirement to present a Cancel control along with any Submit control (I haven't found one yet), but looking in the iOS development guidelines should give you some ideas: