A switch that supports class 3 only means the switch must supply a certain level of power to a given port. It does not mean that it can supply full power to all ports simultaneously.

Having gone through the exercise you are currently working on multiple times, I was already aware of that fact. But thank you for pointing it out for the viewers at home.

Phone systems tend to last a long, long time.

Phone systems last a long, long time...until there is a change in leadership or the ownership of the corporation. You may have Cisco phones deployed at hundreds of sites and then find out your employer has been acquired and the new parent company only uses Avaya. You may hire a new C-level person who has had great results with Cisco or Avaya voice solutions. Out go the Panasonics...

I have no doubt the phone system will outlive the switches.

Having seen some of the weird political shit I've seen in IT during my career, I'd never make such a statement. The wind can change direction overnight. You're using F5 for load balancing today? Rip it out, we're going Citrix Netscaler. You've got Cisco firewalls? Rip them out, we're going Checkpoint. You're using ATT for MPLS? Rip it all out, we're going with Verizon. These changes are rarely based on cold, hard logic.