This is what people forget...your phone can do it all, but your calculator is much more convenient to actually use.
I have a TI-83+ and a TI-89 at home. Admittedly, I haven't used them in a while--I have a HP 12c at my desk, basically always have excel and SAS running (and Tableau too these days), and actually do most quick arithmetic with launchy and alt-space. But, they are great calculators and they are still going strong.
Got the 89 late in high school because it was more fun to play with and had the CAS, but the 83 I have had since the 7th grade is perfectly functional. The key layout is sensible, the menus are navigable, and the low-res screen shows me what I need to know without draining the battery. The 89 is a little better at all of these things (and will pretty-print your inputs), but other than the CAS functions, I can't think of anything that it can do which the 83 cannot.
The 84+ is mostly a logical improvement over the 83. Little more modern look, faster cpu, USB and some more memory (more than enough for what is needed). It does have Mathprint which makes entry a little more like how you would write functions on paper (although I might argue against this..."classic" mode teaches kids how to enter functions with multiple parameters, which is a key lesson for anyone who will later do some simple scripting or even just write excel formulas). They have always felt overpriced, but if they are as durable and long lifed as my 83+, it is not a bad investment. Those calculators have been dropped, abused, and used hard for years without a thought about taking care of them. I owned them before I ever had a cell phone, and I still own them now, None of my phones have lasted that long (not even counting obsolescence...I kept my Razr for years but the keyboard corroded, and my Galaxy S was barely functional at the end of its life between software updates and degraded hardware).
Finally, the HP 12c is still a standard calculator for financial professionals. That thing is even more outddated than the TI-83 and uses RPN which nobody knows how to use, but it still goes for like $80 for the plus model. Similar issues abound: entrenched user base that knows how to use that specific model, lots of hand me down models (mine was made in 1988...2 years after I was born), and several big standardized tests that specify that model (the CFA exams, among others). Truth is, there isn't a ton of complaint from the actual users...because they calculators work great for their intended purpose. The 12c doesn't get complained about because the buyers are the users. The TI graphing calcs are being bought by parents who think "why am I paying so much for an obsolete piece of junk that does less than my kid's cell phone?" without realizing that the calculator does a significantly better job when it comes to features and usability.