Check this out, coming directly from Nintendo UK:
https://www.nintendo.co.uk/Nintendo-Switch/Specifications/Specifications-1176277.html#1
Look at number 6 on that page:
Audio Jack: For connecting commercially available headphones, microphones or headsets
It would seem that you can connect commercially available mics and headsets directly into the Switch. Now, this could be only for games where you can sing into the mic such as Rock Band or Just Dance. However, there are listing for Switch headsets already up for sale, peopel don't typically use those for singing, and likewise those mics have traditionally been through USB connections. Yeah, the Switch itself doesn't have such a port, only the dock does, but who is playing such singing games on the go?
It's my belief that the Switch itself does offer voice chat directly from the unit, but when you're playing on the TV you have to use the Smartphone, plus they're probably pushing the smartphone companion app because it has many features beyond just the voice chat. So they just aren't advertising that you can chat from the device yet. I could be wrong, but there does seem to be some evidence there to back up my claim.