Surface is philosophically the perfect name for a Microsoft Phone, here's why:
many options exist. i feel like microsoft, ever since the surface table unit, wants to name all of its 1st party "devices" surface. bill gates once said that he felt like the future of computing would involve having every SURFACE of a room or office be an interactive computing experience. Microsoft is preparing for that future by naming evrything, the surface coffee table, surface tablet.... surface phone?
remember, the surface tablet is simply called surface, as is the table. he phone would not be surface phone, it would simply be "surface" (because the future of computing, according to bill gates, is every surface is a computer)
a phone or tablet would not be different, it would be the same device jst a different size in the future.