Found nothing out there for the Nexus 5X in terms of nice bumpers for it. Well here you go!
Printed with Ninja - Semi-flex.
Made with Onshape (https://cad.onshape.com/documents/d41aa7947d4a45c403eef770/w/cdb081778b4dcd15109a0791/e/adb412f0a342f69f9861fb23)

I would print it upside down. There's a lip that is best as first layer as the bevel on the bottom layer prevents the need for supports.