The reason to have a dedicated "software design phase" is to encourage invention of "nobody can do it but us" - secret sauces which can make you (or your company) super rich (i.e., algorithms in Oracle Database, Google's algorithms, etc.). These things cannot be invented as "ongoing and continual process".

That doesn't match my experience - and I'm not sure I understand the logic. Why would these algorithms be impossible to development during an incremental process?

From my perspective having a continual software design process, rather than a phased approach, gives me more opportunities for innovative design - not less. We end up doing more software design work that way, since we have the opportunity to add "secret sauce" all of the time - rather than just in some one-off section.

I find I get more innovation out of teams that develop incrementally. That is, to quite a large extent, why we develop that way.