I created a sample here, but the breakpoint for mobile doesn't take effect with code p-xs-5. I have tried 1, 2, 3, 4, 5 and auto, but none of them are working.
<div class="p-5">Text</div>
<div class="p-xs-1">Text</div>
<div class="p-xs-2">Text</div>
<div class="p-xs-3">Text</div>
<div class="p-xs-4">Text</div>
<div class="p-xs-5">Text</div>
<div class="p-xs-auto">Text</div>
Here is the link on codepen to play around