If you're on a first date with someone who is more interested in their phone than you, do you get up and leave?

Depends on context. There are jobs where accessibility in crisis situations is essential -- I lived with a phone or beeper -- pre cellphone days -- growing out of my orifices for 40 years. There are family health situations requiring immediate attention; we're now into the last 20 years of my life as a caregiver. Both are circumstances that should be communicated up front so you can decide whether you want to pursue any kind of date or relationship. If no context has been provided, no satisfactory apology/explanation offered for the interruptions, yeah, it's walking time. Disrespect does not beget respect in return.