not sure if this is still relevant 9 month after you post your question but:
This switch can only provide up to 30W of PoE power coming from a UPOE Parent switch. 22W when powered from the auxiliary 110v power supply. These 22W can be allocated to any of the 8 downlink ports. But the total PoE budget is only 22W. Each one of your 69xx IP phone draws 7W. 7W x 3 = 21W. You are maxed out.
If you need PoE simultaneously on the 8 ports, go with 2960 8PC-L