Based on Thilak's answer I was able to come up with this solution...
Since my form fields only show validation messages if a field is invalid, and has been touched by the user I was able to use this code triggered by a button to show my invalid fields:
// Show/trigger any validation errors for this step_x000D_
angular.forEach(vm.rfiForm.stepTwo.$error, function(error) {_x000D_
angular.forEach(error, function(field) {_x000D_
field.$setTouched();_x000D_
});_x000D_
});_x000D_
// Prevent user from going to next step if current step is invalid_x000D_
if (!vm.rfiForm.stepTwo.$valid) {_x000D_
isValid = false;_x000D_
}
_x000D_
<!-- form field -->_x000D_
<div class="form-group" ng-class="{ 'has-error': rfi.rfiForm.stepTwo.Parent_Suffix__c.$touched && rfi.rfiForm.stepTwo.Parent_Suffix__c.$invalid }">_x000D_
_x000D_
<!-- field label -->_x000D_
<label class="control-label">Suffix</label>_x000D_
<!-- end field label -->_x000D_
<!-- field input -->_x000D_
<select name="Parent_Suffix__c" class="form-control"_x000D_
ng-options="item.value as item.label for item in rfi.contact.Parent_Suffixes"_x000D_
ng-model="rfi.contact.Parent_Suffix__c" />_x000D_
<!-- end field input -->_x000D_
<!-- field help -->_x000D_
<span class="help-block" ng-messages="rfi.rfiForm.stepTwo.Parent_Suffix__c.$error" ng-show="rfi.rfiForm.stepTwo.Parent_Suffix__c.$touched">_x000D_
<span ng-message="required">this field is required</span>_x000D_
</span> _x000D_
<!-- end field help -->_x000D_
</div>_x000D_
<!-- end form field -->
_x000D_