Where you place your mobile form buttons can affect task completion and efficiency. If they’re not in a place where users expect to find them, they could abandon their task and your form.
Even spending a few extra seconds looking for the button can frustrate them and cause them to hit the back button. As soon as they finish filling out the form, you should have the button right in front of them.
Many mobile sites get this wrong when they place their form buttons in the action bar (i.e. navigation bar). Research shows that users often miss submit buttons placed in the action bar (source). It also shows that they miss save buttons in the action bar and exit forms without saving their settings.
