Increased digital security is good, but basing all that on mere possession of a specific phone seems dangerous. For everyone I know, their relationship to their smartphone has been a case of "it's not a matter of 'if' it ever breaks, but rather a case of 'how long until it does?" Whether it is breaking, mysteriously stopping working after an update, getting stolen, compromised by some random free app, getting confiscated... Lots of stuff happens to cell phones, and I'd rather not risk losing my entire digital existence because something happened to it. (I've heard more than one security expert state that they flat out consider their phone to be compromised at any point in time, no matter how new or how recently reset - the only question is "how badly" - and treat it accordingly.)
Case in point: the humble desktop PC. For most people, their desktop or laptop is probably their main backup route to access everything online. (or, for many, probably their *primary* means of doing so). As such, it, at the very least, should not be secured using the thing that it is acting as a backup for.
(Microsoft: Stop trying to force everyone to use microsoft accounts to log into their local computer; especially using their phone based proximity unlock)