NPS surveys generally take the format of:
The touch area of each selection seems to be pretty tight when I put my mockup on a phone... Is there a better design pattern that I could be using here for this type of input?
Other options I considered:
SLIDER
standard slider: http://opinionmeter.com.pk/wp-content/themes/om/images/TouchPointMobileScreeshots/iPadNPS-Large.jpg
fun slider: https://dribbble.com/shots/1641720-NPS-Survey-Interface/attachments/257028
Interaction wise, sliders could work because they can snap to discrete values. The sliding action makes it easier to fine-tune values than tapping since the user can adjust their input provided the slider gives appropriate feedback.
I didn't like this option because sliders tend to have a default starting value and I felt that this would bias the survey and many users may just submit the default value in order to bypass the survey instead of actually making a selection.
PICKER
Pickers tend to have an empty or default field that the user must tap in order to bring up the picker UI. I couldn't think of something reasonable to put in that field... I think the interaction is much more straightforward with the picker than with a slider though...