The RV890 uses cell phone data for Traffic and weather and for map and software upgrades. And it must be connected to the power supply that magnetically holds the unit. A USB cable will not do the job.
I mainly stay out of cities and so we do not especially worry about traffic updates, and I would connect to my phone hotspot for brief periods if I was.
Otherwise for 90% of its functions it does not need the phone.
I was a long time GPS resister preferring software on a notebook, but the RV890 has me converted so far.