What you may need to really achieve a fundamental breakthrough in this technology is a physically small starlink modem with a small antenna, say as large as today's GPS modules.. 
I'm sure they are working on that. but I don't think you really need the bandwidth in such a small device that a huge phase array antenna allows for.
But it will be interesting if they managed to miniaturize a phase array antenna for cellphone use.
For the immediate future it's going to be using something similar to a LTE/5G connection to future generation starlink sats that have advanced cell capabilities.
I think SpaceX have been buying spectrum, so it's probably safe to assume new phones will appear that support some new mobile data standard on a new band that SpaceX will release specs on at some point. I'm thinking we will be seeing new phones with special support for a Starlink cell protocol within 5 years. With faster/better service than the current LTE/5G stuff.
They're goal is definitely going to be selling phone plans for voice/data using the starlink network, they not going to stop at TXT.
It's yet to be seen whether the voice/data plans will be provided though local telcos or directly through a SpaceX/Starlink cell network you pay for in addition to your local carrier fee.