how did i loose my email app on my Iphone 6? how do I get it back??

[iMore Question]

on 12/17 I had my Iphone in my top pocket, while working, later when I checked my phone, I was missing my email, and twitter app that was there earlier. I did not purposefully delete them?? What happened??

 

[JamiePreston]

Mail by Apple
https://appsto.re/us/AFzdcb.i