There's an option on the first screenshot ("ik heb geen smartphone") I don't know what would happen when you click that link (already have my digid on ios set up many years ago) but seems like the government have thought about that.

Of course there is an option not to use a smartphone (for now, and it will not be available if you want to access your medical records after 2020).

The problem lies in the presentation. The styling of the “no smartphone” link is meant to convey that you are doing something undesirable, unsafe, obsolete, weird. That's behavioural nudging. This is fine when the upgrade path is clear and available to all (e.g., “Don't use Internet Explorer, get automatically updating Chrome, Edge, or Firefox”), but it is not fine if the only upgrade path is buying a smartphone and going into an agreement with (foreign) Apple or Google (for the required use of their respective app-stores).

The government should simply not be mandating citizens to own a smartphone just because they can't be arsed to embrace authentication solutions that work on any modern computer (e.g., WebAuthn, or accelerated roll-out of NFC-chip ID-passes and a way to use these with an NFC-reader on any modern OS).