Won't be useable. (i.e. touch); difficult to read (water beads + air pockets).

Personally, (1) I am somewhat jealous -- no enough free time for an extended tour, for the foreseeable future; (2) I tour with a Garmin Fenix 5 mounted on an out-front bar mount. Battery life is much much much better than a phone's (one order of magnitude better). Readable in direct sunlight, much more rugged. I also have a stem mount for my phone, used to navigate cities (the F5 doesn't have mapping capability. TbT navigation with breadcrumb display). More expensive models display maps, but screen size makes it challenging to interpret.

Have tried phone only. Water resistant S7. OK, but useless when it rains hard (drops are interpreted as finger pokes). This + energy requirements makes a phone less than ideal. A dedicated bike computer is more or less a single-use device whereas a smartwatch is useful in different settings (hiking, running, etc.)