I know it's less convenient, but there's dedicated WiFi hotspot devices that exist.
I considered getting a "dumb phone" and one of these devices because in some cases a tablet-style internet-only plan + pay-as-you-go minutes for the odd time I use a phone would be cheaper than a bundled smartphone plan.
At this point saving the $10/month isn't worth the hassle to me though and now I use Slack on my phone so damn much it'd never work :\
Look at the new Nokia 'matrix phone' 8110. It is a dumb phone with some smart features and most notably 4G and WiFi hotspot functionality. At only 80 dollars or so. I am seriously considering getting one just as an experiment
It just doesn't seem to exist.