Phone vs Garmin.
Firstly background, I'm a Technical Director so do know how to use tech as its my bread and butter.
Modern phones are great all round devices and I use both of mine all the time - iPhone 13 (work) Samsung S22 (not-work

) . However the key is in the 'all round' part, its a jack of all trades but a master of none.
I use my iPhone for nav in my ute (pickup) as it has wireless Apple Play and a wireless charger (I don't like connecting cables

). It connects the the dashboard screen and has voice control so simple to use and normally I just want to find some somewhere I've not been to before.
I've also used my previous Samsung and iPhones on the Spyder but they lack the useability I wanted. If I was just doing the same single address navigation I would probably stick with a phone. But instead I want to plan complex routes with multiple checkpoints and shape the route onto preferred, normally bendy, roads etc. I also what something that I can use on the move, e.g. when I have to alternative routes planned and want to change to the second one, and I don't want to be distracted trying to touch small onscreen buttons etc while doing so.
The phone screens, even with with 'touch' gloves, are not really suited to changing things when moving with missed or false clicks etc. The interface designs are for general usage not specific to motorbike use. The routing apps available are all limited in some way with functionality so you end up finding nothing quite does the trick. I'd find one that would support the multi-checkpoint routes I wanted to create then but wouldn't let you change the road preferences for example.
This is why I gave up after a couple of years and bought a Garmin 590 (and just upgraded to a XT). Its pretty much a one trick pony but it does that very well. The interface and screen are specifically designed for gloved hands so using it is not distracting. I can setup routes with multiple checkpoints, I can also add shaping points to force it to use certain roads, I can have multiple routes planned and switch between them.
Its the same with taking photos, most of the time the phones are just great and I use mine all the time but still grab my proper camera when I want to get it right.