I would assume this is just due to the standard apps being really basic, as they are not being well maintained in AOSP as Google and other OEMs have their own. I think there are plans to rewrite the standard apps but I haven't seen any timeline for it and I think the new hardware will be priority (just assuming)
Have you tried other phone apps?
You could try the Fossify Phone App, its simplistic and pretty. If you have other needs you cold try the Google Phone app without network permission (if it lets you)