Phoenix and San Jose are about 614 miles apart by road. Split the difference and you arrive near Las Vegas, the city closest to the halfway point between them. That puts roughly 5 hr 22 min of driving on the Phoenix side and 8 hr 1 min on the San Jose side — the fairest single meeting point among the cities near the middle.
That's a half-day drive from each side, so Las Vegas suits an overnight or a weekend rather than a quick coffee — long enough to want a reason to stay, short enough to drive.
If Las Vegas doesn't have what you're after, Los Angeles and San Diego are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Phoenix and San Jose.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.