You probably just need to adjust the allocated power per slot for that card. I think the default is only like 75W per blade. You can configure it higher.
From Concepts Guide for Exos 12.4, but applicable to earlier releases:
On modular PoE switches, you reserve power for a given slot. The power reserved for a given slot
cannot be used by any other PoE slots, even if the assigned power is not entirely used. To reallocate
power among the slots, you must reconfigure each slot for the power budget you want; the power is
not dynamically reallocated among PoE modules.
On modular switches, the default power budget is 50 W per slot, and the maximum is 768 W. The
minimum reserved power budget you can configure is 37 W for an enabled slot. If inline power on the
slot is disabled, you can configure a power budget of 0.
configure inline-power budget <num_watts> {slot <slot>}
num_watts - Specifies the number of watts to reserve for specified switch or slot for inline power. Enter an integer. The minimum value is 37, or 0 if the slot is disabled; the maximum is 768; and the default value is 50.
slot - Specifies a slot. The slot must be configured to hold a PoE module.
I would try bumping it up to 100W from the default and then try plugging more phones in. They'll power up. I'm sure that you are over the default 50W. It only takes about 10 phones or so to hit the maximum. When you plug phones in beyond the budget they will not power up.
