Thanks for the update!
The way to sync contact categories as a new contact or as categories is selectable in DavX5, before initial sync
You can also change it at a later time in the account settings. Which method is the right one for SmarterMail, according to your tests?
The customizable phone numbers labels are not supported by SM. Unfortunately, I added one on my phone, synced it to SM and the default ‘Home’ phone number was also lost
Those things are supported well by DAVx⁵, while many servers have problems with that. So I guess these are missing features in SmarterMail. If there is any specific thing you’re missing in DAVx⁵, please let us know.
SM has separate fields for Address, City, State, Country but after sync, all the address fields were concatenated and added in the ‘Home Address’ field.
Does this help? https://www.davx5.com/faq/entering-structured-addresses