PDF Form fillable in phone browser?

So, I would say I'm a pretty advanced Acrobat user. But I've run into something that just surprised me and has me stumped.

I've created a PDF form (a job application). I fully expected to be able to upload it to my web server, put a link in my job postings, and have folks fill out the application on their web browsers using whatever device they have in front of them. I was shocked to discover that, while the form is fillable in a desktop web browser and the Reset button works, simple calculated fields and the Submit button do nothing. On a phone browser, the form is not even fillable.

I tried using Acrobat DC's Fill and Sign tool to see if that made any difference, but it won't work in this case because I need anyone to be able to fill the form and send it. Fill and Sign seems to require the form to be "assigned" to specific people by email.

I then tried uploading the PDF form to Document Cloud and sharing it via link from there, but the form isn't fillable that way either.

What am I missing? Anyone have advice?